Salmonellosis (foodborne diseases). Diagnosis of Salmonella food poisoning Serological classification of Salmonella according to White and Kauffmann

Diseases of people with a clinical picture of poisoning resulting from eating meat and other animal products have been known for a long time. However, the essence of their occurrence before the 80s. In the 19th century, opinions and theories varied.

The bacterial etiology of toxic Salmonella infections was first substantiated by A. Gertner in 1888. During an outbreak of human disease, he isolated identical bacteria from the meat of a forcedly slaughtered cow and from the spleen of a deceased person, which later received the name Gertner’s bacillus.]

Subsequently, a theory emerged that suggested the cause of poisoning was copper salts, the source of which was poorly tinned utensils for preparing and storing food. With the discovery of toxic substances formed in rotting meat, and in particular ptomaines, they began to be seen as the culprits of “meat poisoning.” However, all these theories about the causes of “meat poisoning” turned out to be unreliable.

The bacterial theory of foodborne diseases began to take hold in the second half of the 19th century. The first reports were made in 1876 and 1880. O. Bollinger. He analyzed 17 outbreaks of foodborne diseases, affecting 2,400 people and with 35 deaths, and found that all these cases of disease were associated with eating meat from animals forcedly killed due to gastroenteritis and septic-pyemic processes.

In parallel with the discovery of causative agents of foodborne toxic infections in humans, causative agents of various diseases in animals were discovered. Even before Gertner’s discovery, in 1885, the American microbiologist D. E. Salmon isolated a bacillus called Vas from the meat and internal organs of swine fever patients. Suipestifer, later named S. choleraesuis. At first, this microbe was considered as the causative agent of swine fever and only later was recognized as a companion to this disease, which has a viral etiology.

All these bacteria turned out to be very close to Gärtner's bacillus and to each other in their morphological and biological properties. Due to this commonality, all these bacteria were combined into one paratyphoid-enteric genus, and the diseases they caused in animals began to be called paratyphoid fever. In 1934, at the proposal of the nomenklatura-

The Noah Commission of the International Congress of Microbiologists decided to name the mentioned genus “Salmonella” (Salmonella). This is how the memory of the microbiologist Salmon was immortalized, who was the first researcher to discover in 1885 one of the representatives of this genus of bacteria - B. choleraesuis.

CHARACTERISTICS OF BACTERIA OF THE GENUS SALMONELLA

Salmonella is one of 12 genera of the large family of bacteria Enterobacteriacae. To date, about 2000 Salmonella serovars have been systematized using serological typing. They are found (live) in the intestinal canal of animals and humans, as well as in the external environment. Morphologically they are small rods with rounded ends, sometimes oval in shape. All of them, except A. vullorum and S. gallinarum, are well motile, Gram stained negatively, and do not form spores or capsules. They are aerobes or facultative anaerobes. The optimal reaction of the growth medium is slightly alkaline (pH - 7.2-7.5), the optimal growth temperature is 37 ° C, although salmonella grow well at room temperature, their growth at low temperatures above zero (5...8 ° C) is not excluded ).

Salmonella has the property of producing endotoxins. The latter are glucido-lipoid-polypeptide complexes, identical to the somatic antigen of bacteria, and are thermostable. Numerous experiments have shown that when administered parenterally they are highly toxic. Thus, a dose of 0.3 ml of a filtered 7-day liquid culture when administered subcutaneously causes the rapid death of mice. At the same time, 10-30-fold doses when administered enterally did not cause disease in animals. The same was confirmed in experiments on monkeys. Finally, people voluntarily, as a self-experiment, drank from 20 to 350 ml of salmonella toxins (filtrate of a killed culture) before meals, and they did not get sick. Based on these experiments, it was concluded that Salmonella does not have enterally acting toxins, and foodborne toxic infections in humans are caused only by living bacteria.

There are two methods for typing (i.e. establishing the species) of bacteria of the genus Salmonella: serological and biochemical. For serological typing, an agglutination reaction (RA) is used with polyvalent and monoreceptor Salmonella sera.

Biochemical typing is based on the difference in the composition of enzymes in Salmonella. Due to enzymatic (biochemical) differences, some bacteria are able to decompose certain carbohydrates or alcohols, while others do not have this ability. Various selective media are used for biochemical typing

(Endo, Smirnova, Levina, Ploskireva, etc.). One of the most commonly used is the Endo elective medium. The ingredient in Endo medium is lactose sugar, and the indicator is fuchsin, decolorized with sodium sulfide. Coliform bacteria decompose lactose, but Salmonella bacteria do not decompose lactose. When bacteria of the genus E. coli grow on Endo medium, due to the decomposition of lactose and the formation of lactic acid, the red color of fuchsin is restored, which does not happen during the growth of salmonella. In this regard, colonies of intestinal bacteria on Endo medium will be red-violet with a metallic sheen, and the medium around the colonies will turn red; salmonella grow on this medium in the form of translucent colonies of light pink color with a bluish tint.

For further biochemical typing of Salmonella, a small or large variegated range of media is used. The motley series includes Hiss media with various sugars and polyhydric alcohols, as well as broth with glycerin (according to Stern), medium with rhamnose (according to Bitter), milk, litmus milk and meat-peptone broth with indicator paper (for hydrogen sulfide) . During biochemical typing, in addition to changing the color of media, the ability of bacteria to form hydrogen sulfide, indole, etc. is studied.

The belonging of a culture to a certain type of bacteria based on changes in media of a variegated series is established using tables or determinants that are available in textbooks for practical exercises in veterinary examination. Consequently, typification of bacteria of the genus Salmonella and determination of their species are possible only as a result of bacteriological research.

Bacteriological examination of meat and meat products to identify their contamination with bacteria of the genus Salmonella, as well as opportunistic bacteria, staphylococci, streptococci and anaerobes is carried out in accordance with GOST 21237-75. "Meat. Methods of bacteriological analysis". For bacteriological examination, a part of the flexor or extensor muscle of the front and hind limbs of the carcass with a length of at least 8 cm or a piece of another muscle measuring at least 8 x 6 x 6 cm is sent to the laboratory. Lymph nodes (superficial cervical, external iliac, and in pigs and submandibular), liver lobe with hepatic lymph node and emptied gall bladder, kidney and spleen.

When examining salted meat in a barrel container, samples of meat and existing lymph nodes are taken from the top, middle and bottom of the barrel, as well as, if present, a long bone. Samples are wrapped in waxed or parchment paper, labeled, numbered, wrapped in a single bag, tied with twine, sealed or sealed with a wax seal. From the material sent to the laboratory, fingerprint smears are prepared according to the generally accepted method, stained with Gram and examined microscopically, and also inoculated on meat-extract agar and the above-mentioned selective media. To identify and isolate a pure culture of Salmonella in laboratories, accumulation media (selenite and magnesium media) are widely used. When carrying out bacteriological research, methods of serological and biochemical typing are used in combination.

PATHOGENICITY OF BACTERIA

GENUS SALMONELLA

FOR ANIMALS

The pathogenic effect of Salmonella on animals occurs when complex mechanisms between micro- and macroorganisms are disrupted. Pathogenicity degree

The strain depends on the type of Salmonella, the infectious dose, the biological characteristics of the pathogen, as well as the age of the macroorganism, its resistance and other factors. To date, a sufficient amount of data has accumulated in the literature indicating the inconsistency of distinguishing Salmonella into pathogenic only for humans, animals or birds.

In animals and birds under natural conditions, salmonella are the causative agents of infectious diseases called salmonellosis. In accordance with the pathogenesis and epizootological characteristics, these diseases are divided into primary and secondary salmonellosis.

With these factors, the virulence of Salmonella increases, they multiply intensively and penetrate from the places of initial localization (intestines, liver, mesenteric lymph nodes) into various organs and muscles. In this regard, pathological and anatomical changes can be very diverse and are largely determined by which primary pathological process the secondary salmonellosis was superimposed on. Hemorrhages in various organs, especially

PATHOGENICITY OF BACTERIA

GENUS SALMONELLA

FOR PEOPLE

The incubation period is on average 12-24 hours, but sometimes lasts up to 2-3 days.

The gastroenteric form is manifested by increased body temperature, chills, nausea, vomiting, loose stools, sometimes mixed with blood and mucus, abdominal pain, increased thirst and headaches. The disease develops especially severely, with symptoms of uncontrollable vomiting and even damage to the nervous system, when S. typhi-murium enters the human body with food.

The typhoid-like form can begin with ordinary gastroenteritis and, after an apparent temporary recovery, after a few days it manifests itself with signs characteristic of ordinary typhoid fever.

The influenza-like form, quite common in human illness, is characterized by pain in the joints and muscles, rhinitis, conjunctivitis, catarrh of the upper respiratory tract and possible gastrointestinal disorders.

The septic form occurs in the form of septicemia or septicopyemia. In this form, local septic processes caused by Salmonella are observed with localization of foci in internal organs and tissues: endocarditis, pericarditis, osteomyelitis. arthritis, abscesses, etc.

The mortality rate from foodborne illnesses averages 1-2%, but depending on the severity of outbreaks, the age composition of people (the disease among children) and other circumstances, it can reach up to 5%.

EPIDEMIOLOGY OF FOOD SALMONELLOSISES

The leading role in the occurrence of food salmonella belongs to meat and meat. Particularly dangerous in this regard is meat and offal (liver, kidneys, etc.) FROM forcedly killed animals. Intravital contamination of muscle tissue and organs with Salmonella occurs as a result of animal disease with primary and secondary salmonellosis. Dangerous food products from the point of view of the occurrence of foodborne salmonellosis include minced meat, jellies, brawn, low-grade (separate, table, liver, blood, etc.) sausages, meat and liver pates. When grinding meat into minced meat, the histological structure of the muscle tissue is disrupted, and the flowing meat juice contributes to the dispersion of salmonella throughout the fatpa and their rapid reproduction. The same applies to pates. Jellies and brawns contain a lot of gelatin, and low-grade sausages contain a significant amount of connective tissue (pH 7.2-7.3). In other conditions, salmonella also develops very quickly. Waterfowl are often Salmonella carriers, and, therefore, their eggs (ducks, geese) and meat can be a source of foodborne salmonellosis.

Food products. Sources of exogenous contamination can be various environmental objects: water and ice, containers, knives, tables, production equipment, with the help of which primary processing and processing of products is carried out; The participation of biological agents in the contamination of products with Salmonella (mouse-like rodents, flies) is also not excluded. A contact route of infection with Salmonella according to the “animal (bacteria-excreting)-human” scheme cannot be ruled out. Indoor animals (dogs, cats), as well as pigs, poultry and even pigeons play a certain role in this. The contact factor of transmission according to the “person-to-person” scheme is a rare phenomenon and occurs more often in children.

PREVENTION OF FOOD SALMONELLOSISES

Success in the fight against salmonellosis and its prevention is inextricably linked with the need to fully strengthen measures aimed at neutralizing the sources and factors of transmission of infection, which specialists from medical, veterinary, veterinary-sanitary and other departments are called upon to carry out on the basis of clear coordination of their actions.

The causative agents of salmonellosis are other serotypes of salmonella that are pathogenic for humans and animals (S.typhimurium, S.enteritidis, S.heldelberg, S. newport and others). The pathogenesis of salmonellosis is based on the action of the pathogen itself (its interaction with the host body) and endotoxin that accumulates in food products infected with salmonella. In the classic version, Salmonella toxicoinfection is gastroenteritis. However, when the intestinal lymphatic barrier breaks, generalized and extraintestinal forms of salmonellosis can develop (meningitis, pleurisy, endocarditis, arthritis, liver and spleen abscesses, pyelonephritis, etc.). The increase in generalized and extraintestinal forms of salmonellosis is associated with an increase in the number of immunodeficiency states, which is of particular importance in HIV infection.

A separate problem is posed by hospital strains of Salmonella (usually individual phages of S.typhimurium), which cause outbreaks of nosocomial infections mainly among newborns and weakened children. They are transmitted mainly through contact and household contact from sick children and bacteria carriers; they are highly invasive, often causing bacteremia and sepsis. Epidemic strains are characterized by multiple drug resistance (R-plasmids), high resistance, including to high temperatures.

Salmonella foodborne toxic infections occur after consuming food products heavily contaminated with salmonella (the infectious dose must be massive). The disease develops a few hours after ingestion of poor quality food as gastroenteritis with diarrhea, vomiting and is accompanied by severe intoxication (sometimes very severe). The disease lasts 3-7 days. Bacteria are released during the disease and for some time after clinical recovery. After an illness, a bacteria carrier may form, especially if the pathogen enters the liver (bile ducts, gallbladder).

Foodborne toxic infections are most often caused by salmonella belonging to serogroups B, C, D, E. All of them have a reservoir among animals and birds, i.e. These diseases are zoonotic. The most common pathogens of PTI are:

S.typhimurium (group B) - the source of infection can be mice, pigeons, poultry and their eggs. Other products may be secondarily contaminated.

S.choleraesuis (group C) - the source of infection is pigs.

S.enteritidis (group D) - source of infection - cattle.

Salmonellosis is characterized by epidemiological features. The first feature is the polypathogenicity of pathogens, which results in an extraordinary variety of reservoirs and possible sources of infection. These include cattle, calves, piglets, chickens, ducks, geese, rodents - beauties, mice. In animals, Salmonella can form an asymptomatic or clinically significant infection.

The second epidemiological feature is the multiplicity of transmission routes and factors. The main route of infection for salmonellosis is nutritional, and the transmission factors are various food products of animal origin (meat, meat products, eggs, egg products, milk and dairy products). Water can serve as a direct or indirect factor. People become infected from sick animals while caring for them.

The third feature is that the nature of the occurrence of epidemic outbreaks of salmonellosis has changed, resulting from the entry into the distribution network of various food products contaminated with salmonella, as a result of which their epidemiological decoding is difficult.

The next epidemiological feature is polyetiology. The number of serological variants of Salmonella isolated from humans and animals increases every year.

Pathogenicity factors.

Salmonella has adhesion and colonization factors and invasion factors. They have an endotoxin with a wide spectrum of action; many Salmonella have enterotoxins (LT and/or ST toxins), which disrupt the functions of the adenylate and guanylate cyclase systems of enterocytes, respectively, which leads to disruption of water-salt metabolism and the development of diarrhea. Some salmonella have a cytotoxin that disrupts protein synthesis in enterocytes, which causes hypersecretion and impaired enterosorption of fluid in the small intestine and, as a result, diarrhea develops.

Pathogenesis

In the pathogenesis of foodborne toxic infections, the ingestion of a large number of pathogens and their endotoxin with food is important. Having attached to the intestinal epithelium, salmonella begin to multiply, penetrate into the submucosal space and into the lymphatic formations in the intestinal wall, where they further multiply and die with the release of endotoxin. Massive accumulation of endotoxin (together with endotoxin introduced from the outside) leads to intoxication, often severe with fever, disorders of the nervous and vascular systems, including collapse and diarrhea.

With fewer salmonellae entering the body with food, the disease can occur in the form of gastroenteritis with diarrhea, but without severe intoxication and without a rise in temperature.

Those who have recovered from salmonellosis do not acquire strong immunity; prolonged carriage of the bacteria and repeated diseases are possible. Local immunity is characterized by increased accumulation of SIgA. Immunity is variant specific.

Salmonellosis with generalization of the infectious process. This is an acute intestinal infection with a long, severe course of the type of typhoid or toxic-septic infection (with the development of secondary purulent foci in various organs). This form of the disease is typical for young children, but sometimes occurs in adults with a weakened immune system. Infection occurs not only through food products (a small infectious dose is sufficient), but also from bacterial carriers through contact and household contact. The most frequently isolated pathogen is S. typhimurium.

Often salmonellosis, including generalized ones, occurs in hospital settings as nosocomial infections. The main causative agents of generalized salmonella infection are hospital strains of S. typhimurium, adapted to the human body. They have all the pathogenicity factors characteristic of S.tuphimurium, but as hospital strains, they are characterized by increased virulence, long-term persistence on environmental objects and are resistant to many antibiotics.

Laboratory diagnosis of salmonella infections is carried out similarly to the microbiological diagnosis of typhoid fever and paratyphoid fevers A and B.

For food poisoning, the main method of diagnosis is bacteriological, and in parallel with materials from the patient, food products that were the suspected cause of the disease are also examined. For generalized salmonellosis, both bacteriological (with blood culture isolation) and serological research are carried out.

Salmonella. Food poisoning caused by bacteria of the genus Salmonella ranks first among microbial food poisonings. The microbes were named after the American microbiologist D. Salmon, who first identified one of the representatives of this group in 1885.

The genus Salmonella belongs to the Enterobacteriaceae family of intestinal bacteria. Currently, over 2.5 thousand serological variants (serovars) have been described, of which more than 700 have been isolated from humans. The most common are 15-20 variants of pathogens, including Salmonella murine typhus (S. typhimurium), enteritis (S. enteritidis) , swine cholera (S. choleraesuis), etc.

In the latest edition of Bergey's Guide to Bacteria (1994), all Salmonella are classified into two species. The species Salmonella bongori contains less than 10 very rare serovars (species in previous editions).

All the remaining 2500 serovars, previously called species, are included in the species Salmonella choleraesuis, which, according to phenotypic and genetic criteria, is divided into 6 subspecies: S. choleraesuis subsp. arizonae, S. choleraesuis subsp. choleraesuis, S. choleraesuis subsp. diarizonae, S. choleraesuis subsp. houtenae, S. choleraesuis subsp. indica, S. choleraesuis subsp. salamae

The subspecies includes various serovars, which within the subspecies choleraesuis have names, while in other subspecies the serovars do not have names, with the exception of some serovars in the subspecies salamae and houtenae.

In the antigenic formula, the presence and quantity of various groups of antigens (somatic O-antigen, flagellar H-antigen, envelope or capsular K-antigen, Vi-virulence antigen, etc.) are noted using symbols.

The subspecies S. choleraesuis subsp. choleraesuis included serovars (formerly species): choleraesuis, gallinarum, paratyphi A, pullorum, typhi.

Bacteria of the genus Salmonella are small gram-negative rods. Cells have an average length of 2 to 5 microns and a width of 0.6 microns. Most Salmonella species are motile, have peritrichous flagella, and do not form capsules or spores (Fig. 36).

Salmonella grows well on ordinary nutrient media, facultative anaerobes. Optimal growth is observed at a temperature of 37 °C.

On MPB, salmonella cause turbidity; on MPA, they form colonies of medium size (2-3 mm in diameter), difficult to distinguish from colonies of coliform bacteria. Freshly isolated strains form round, smooth, shiny colonies (Figure 36). Salmonella ferment glucose, maltose, mannitol and sorbitol to produce acid and often gas.

Figure 36 - Salmonella paratyphy: A- colonies; b - cells

Salmonella are chemoorganotrophs and have both respiratory (using oxygen) and fermentative (dehydrogenation) types of metabolism. They produce the enzyme catalase and hydrogen sulfide. Indole is not formed. The methyl red test is positive. Found in humans, warm- and cold-blooded animals, and in food products. Pathogenic to humans and many animal species.

In addition to food toxic infections, they cause typhoid fever, paratyphoid fever and septicemia.

They do not form spores, but are relatively highly resistant to various physical and chemical environmental factors, as well as antibiotics. They tolerate drying well, remaining at room temperature on various substrates for 2.5-3 months; in dried animal feces - for 3-4 years. In frozen vegetables (at minus 18 ° C), salmonella persist for 2-2.5 years.

In dairy products, these microbes not only persist for a long time (up to 3-4 months), but also multiply without changing the appearance and taste of the products. Salmonella is detected in oil within 4 months. when stored at room conditions and 9-10 months. - in a refrigerator. In cottage cheese, the viability of salmonella is the highest - up to 34 months. In water, especially with a low pH value, salmonella survive up to 2 months.

Milk pasteurization modes are sufficient to inactivate Salmonella if their initial concentration does not exceed 3 x 10 12 cells per 1 cm 3 of milk.

The main sources of salmonella infection are agricultural and domestic animals, birds.

Salmonella contamination of food products can vary. If milk is infected directly from sick animals, then such infection is called primary. Secondary infection of products occurs when they are improperly processed, stored, or transported.

Prevention of foodborne toxic infections should include measures aimed at eliminating salmonella infection, as well as compliance with sanitary and hygienic conditions when receiving milk, transporting and storing dairy products.

Escherichia coli genus Escherichia (Escherichia). Being permanent inhabitants of the intestines of humans and animals, bacteria of the genus Escherichia (E. coli) under certain conditions acquire pathogenic properties and become causative agents of various pathological processes. They cause colibacillosis in young animals, colienteritis in children, cause mastitis, etc.

There are varieties of Escherichia: enteropathogenic, enterotoxigenic, enteroinvasive and enterohemorrhagic.

The type species of the genus Escherichia is E. coli; in addition, this genus includes four more species: E. fergusonii, E. hermanii, E. vulneris and E. blattae, which differ in biochemical and serological characteristics.

Escherichia coli that cause foodborne illnesses are called enteropathogenic. They are often found in dairy, meat and other products, but they cause food poisoning relatively rarely. This is explained by the fact that Escherichia do not always accumulate in products in the amount necessary for the occurrence of the disease, and most importantly by the fact that relatively few strains of Escherichia coli are pathogenic for humans.

Sources of pathogenic strains of E. coli are sick animals, as well as people who violate the sanitary and hygienic regime in the production of dairy products.

The main toxin of Escherichia is a heat-stable endotoxin that can withstand heating up to 90-100 °C. It is a type-specific endotropic poison.

E. coli do not have pronounced resistance. They are neutralized during milk pasteurization. At 60 °C they die after 15 minutes; a 1% phenol solution causes the death of microorganisms after 5-15 minutes.

To prevent food poisoning caused by E. coli, it is necessary to observe the rules of personal hygiene by dairy industry workers, improve the sanitary culture of the population, and prevent fecal contamination of water and food products.

Bacteria of the genus Proteus (Proteus) include four species (P. vulgaris, P. mirabilis, P. myxofaciens, P. penned) belonging to the family Enterobacteriaceae.

These are straight polymorphic rods, 0.4-0.8 x 1-3 µm in size, gram-negative, motile due to peritrichial flagella, do not form spores or capsules (Figure 37).

In relation to oxygen, bacteria of the genus Proteus are facultative anaerobes, and in terms of the type of metabolism they are chemoorganotrophs, having both respiratory and fermentative types of metabolism. The optimal development temperature is 37°C. Most strains do not form colonies on solid nutrient media. They grow in the form of a thin veil-like coating with the formation of concentric zones or

Figure 37 - Proteus vulgaris

spread over the moist surface of the nutrient medium in the form of a homogeneous film.

Bacteria ferment glucose to produce acid and often gas. Some species ferment glycerol, D-xylose, maltose, sucrose and trehalose.

Rods of the genus Proteus carry out. oxidative deamination of phenylalanine and tryptophan, hydrolyze urea. Usually they form hydrogen sulfide, sometimes indole, and reduce nitrates.

They are found in the intestines of humans and various animals, as well as in manure, soil, polluted waters, and rotting organic substrates. The species P.myxofaciens was isolated only from the gypsy moth larva.

Many strains of bacteria of the genus Proteus are pathogenic for humans: in addition to foodborne infections, they can cause urinary tract infections, as well as secondary lesions leading to the formation of septic lesions, especially in burns.

The most common causative agent of food poisoning is Proteus vulgaris. It is widespread in nature - in soil, water, the contents of the gastrointestinal tract, as well as in rotting organic substrates.

The source of food poisoning is food consumed by humans, which is abundantly contaminated with these microorganisms.

Many strains of Proteus vulgaris form heat-stable endotoxins, which are glucido-lipoid-polypeptide complexes with hemolytic activity. .

Food poisoning is also caused by the action of highly active enzymes secreted by P. vulgaris and promoting the accumulation of toxic breakdown products of proteins - amines. .

Bacteria of the genus Proteus are resistant to low temperatures and can withstand alternating freezing and thawing three times. Milk pasteurization modes neutralize the pathogen; a 1% phenol solution causes the death of Proteus bacilli after 30 minutes.

Prevention of foodborne infections caused by bacteria of the genus Proteus is the same as for foodborne infections caused by bacteria of the genus Escherichia.

Clostridia perfringens (CI. perfringens). Toxic infections caused by Cl. perfringens, occupy third place after food poisoning of salmonella and staphylococcal origin.

The name of the pathogen is associated with the ability to form large amounts of gas, which ruptures the surrounding dense nutrient medium. The term “perfringens” translated from Latin means “breaking through”, “breaking through”, “making way by force”.

Species Cl. perfringens is divided into 6 serovars: A, B, C, D, E and F, which differ in their antigenic properties and the specificity of the toxins they produce.

Clostridia are large, non-motile gram-positive rods. In the body of humans and animals they form a capsule. Slowly form spores (Figure 38).

Cl. perfringens is an anaerobe, but can grow in the presence of small amounts of oxygen. Microorganisms of this species grow well on meat and casein nutrient media. Rapid growth is observed on media containing glucose, lactose, maltose or mannose. On solid nutrient media they form smooth (S), rough (R) and slimy (M) colonies ranging in size from 1 to 5 mm. Cl perfringens develops at temperatures from 15 to 50 °C. The optimal temperature for the fastest growth is 37 °C.

A special feature of O. perfringens is its ability to reproduce rapidly. Its regeneration duration is 10 minutes. When growing in milk, it forms a curd and a large amount of gas (foam).

The pathogen ferments glucose to form salts of lactic, acetic and butyric acids, ethyl alcohol, carbon dioxide and hydrogen, and can ferment fructose, galactose, mannose, maltose, lactose, sucrose, ribose, starch, dextrin and glycogen. Glycerol fermentation is inconsistent, and mannitol is not fermentable.

Cl. perfringens produces hydrogen sulfide and does not form indole. Most strains reduce nitrates to nitrites and liquefy gelatin. It produces several types of toxins. Enterotoxin is produced by certain strains of serovars A, C and D. It is a protein with a molecular weight of 36,000. It contains 19 amino acids, the dominant ones being aspartic acid, serine, leucine and glutamic acid. This is a heat-labile toxin, which at a temperature of 60 ° C is inactivated by 90% in 4 minutes, i.e. its amount decreases 10 times.

Enterotoxin is produced by Cl cells. perfringens during spore formation. Vegetative forms of the pathogen are sensitive to oxygen, sunlight, high temperature, acids, disinfectants, as well as many antibiotics acting on gram-positive bacteria. They are sensitive to low temperatures (susceptible to cold damage at all

stages of growth. Spores are more stable than vegetative cells. When boiled, they die within 15-30 minutes.

Cl. perfringens is widely distributed in soil and intestinal contents and can therefore contaminate many foods.

Prevention of food poisoning caused by Cl. perfringens, includes the same measures as for foodborne infections caused by salmonella and E. coli.

Bacillus cereus- the Latin word “cereus” means “waxy”, apparently referring to large sticks with chopped ends, reminiscent of wax candles (Figure 39). Its main habitat is soil with a neutral or slightly alkaline reaction, from which it enters the air and water, and then onto food products. The microbe can cause mastitis in cows.

As a result of the release of the lecithinase enzyme by this microorganism, lecithin breakdown products (phosphocholine, etc.) are formed, which have a toxic effect on the macroorganism.

Toxic infections are also caused by the formation of thermostable enteropathogenic and thermolabile neurotropic endotoxins by Bac.cereus.

The microorganism forms spores and is therefore highly resistant. It is often (up to 86%) found in pasteurized milk, canned milk and meat. Can develop when the concentration of table salt in the substrate is up to 10-12 %, sugar up to 30-60 %. On your life activity. cereus is negatively affected by the acidic reaction of the environment. Products with a pH of 4.5 and below are an unfavorable environment for the development of these microorganisms.

Prevention is aimed at eliminating the causes that contribute to getting you. cereus into milk and dairy products from soil, air and water.

Date added: 2015-09-03 | Views: 1181 | Copyright infringement

Brief historical background. Diseases of people with a clinical picture of poisoning resulting from eating meat and other animal products have been known for a long time. Until the 80s of the last century, opinions and theories varied about the reasons for their occurrence. At one time, the cause of “meat poisoning” was considered to be hydrocyanic acid, which under certain conditions can form in meat. Subsequently, a theory emerged that suggested the cause of poisoning was copper salts, the source of which was poorly tinned utensils for preparing and storing food. With the discovery of toxic substances formed in rotting meat, in particular ptomaines, they began to be seen as the culprits of “meat poisoning.” However, all these theories turned out to be unreliable. The bacterial theory of foodborne diseases began to take hold in the second half of the last century, and it was first substantiated by Gertner in 1888. During an outbreak of human disease, he isolated identical bacteria from the meat of a forcedly slaughtered cow and from the spleen of a deceased person, which later received the name Gertner’s bacilli, Based on his experiments, this scientist came to the conclusion that the stick he isolated is capable of forming heat-stable toxic substances, the presence of which in the product causes the occurrence of foodborne illness. According to Gertner, toxic substances formed in food products when they are contaminated with bacteria act enterally and cause diseases without the participation of living pathogens. This view, refuted only very recently, has greatly delayed the development of our knowledge in this area (I. S. Zagaevsky).

The following years were marked by the discovery of other bacteria, which also turned out to be responsible for outbreaks of foodborne illnesses in humans and were similar in morphological and biological properties to Gärtner's bacillus. Thus, in 1893, a bacterium named B. enteritidis Breslau was isolated from a foodborne illness in Breslau. In 1900, Schotmuller and Kurt, during mass diseases of people clinically similar to the picture of typhoid fever, isolated a bacterium very close to the Gärtner and Breslau bacillus, which was named B. paratyphi B. In 1899, before the discovery of B. paratyphi B, the culprit of typhoid-like human diseases, a microorganism was identified, which was named B. paratyphi A, etc.

In parallel with the discovery of pathogens of foodborne diseases in humans, pathogens of various diseases in animals were discovered. In 1885, from the meat and internal organs of swine fever patients, the American microbiologist Salmon isolated a bacillus called B. suipestifer, later called S. choleraesuis. At first, this microbe was considered as the causative agent of swine fever, and only later was it recognized as a companion to this disease, which has a viral etiology.

In 1893, B. typhimurium, the causative agent of the typhus epizootic of house mice, was discovered, which later turned out to be identical with the Breslau bacillus. In 1897, our compatriot Isachenko isolated the causative agent of the rat epizootic, which turned out to be a variety of B. enteritidis Gartneri and was named B. enteritidis var ratin. In 1893, the causative agent of infectious abortion of mares-B was discovered. Abortus equi, in 1910, 2 variants of bacteria that cause typhus in piglets (B. typhi suis glasser and voldagsen), similar in their properties to B. cholerae suis (S. suipestifer), were isolated, and in 1926 B. abortus ovis - causative agent of sheep abortion, etc.

All these bacteria turned out to be very close to Gärtner's bacillus and to each other in their morphological and biological properties. Due to this commonality, all these bacteria were combined into one paratyphoid-enteric genus, and the diseases they caused in animals began to be called paratyphoid fever. In 1934, at the proposal of the nomenclature commission of the International Congress of Microbiologists, it was decided to call the mentioned genus “Salmonella” (Salmonella). This is how the memory of the microbiologist Salmon was immortalized, who was the first researcher to discover in 1885 one of the representatives of this genus of bacteria - B. cholerae suis (S. suipestifer).

General characteristics of salmonella bacteria. Salmonella is one of 12 genera of the large family of bacteria Enterobacteria cae. To date, more than 2000 Salmonella serotypes have been systematized using serological typing. They are found (live) in the intestinal canal of animals and humans, as well as in the external environment, i Morphologically they are rods with rounded ends, sometimes oval in shape, their length is 2-4 and their width is 0.5 microns. All of them, with a few exceptions (S. pullorum, S. gallinarum), are motile, gram-negative, and do not form spores or capsules. They are aerobes or facultative anaerobes. The optimal reaction of the growth medium is slightly alkaline (pH 7.2-7.5), and the growth temperature is 37 °C. True, salmonella grow well at room temperature, and their growth at low temperatures above zero (5-8°C) cannot be ruled out. Salmonella are almost indistinguishable by growth on plain agar and ordinary liquid nutrient media. On meat-peptone agar, smooth - S-forms of these bacteria form round, translucent, convex, sometimes with a slightly depressed center, and moist colonies with a slight metallic sheen; rough-R-forms have the appearance of unevenly rounded, rough, dull and dry colonies. On slanted agar they grow luxuriantly, forming strong turbidity in condensation water; on meat-peptone broth they cause uniform turbidity of the medium; gelatins do not liquefy, do not form indole, and milk is not fermented.

Salmonella is quite resistant. They can live for a long time in dust, dried feces and manure, in soil, water and animal feed, maintaining virulence. It has been established that during biothermal disinfection of manure, salmonella are inactivated only within 3 weeks. To completely disinfect meat contaminated with salmonella, it is necessary to bring the temperature inside the pieces to 80 °C and maintain it at this level for at least 10 minutes. In frozen meat, salmonella remain viable for 2-3 years. In salted meat they remain viable for 5-6 months, and when the product contains 6-7% NaCl, they can even multiply.

Salmonella has the property of producing endotoxins. The latter are thermostable and represent glucido-lipoid-polypeptide complexes identical to the somatic antigen of bacteria. Numerous experiments have established that when administered parenterally they are highly toxic. Thus, a dose of 0.3 ml of a filtered 7-day liquid culture when administered subcutaneously causes the rapid death of mice. At the same time, 10-30-fold doses greater than the previous ones did not cause disease in animals when administered enterally. The same was confirmed in experiments on monkeys. Finally, people voluntarily, as a self-experiment, drank from 20 to 350 ml of salmonella toxins (filtrate of a killed culture) before meals, and they did not get sick. Based on these experiments, it was concluded that Salmonella does not have enterally acting toxins, and only live bacteria cause foodborne illnesses in humans.

Along with the great commonality of morphological and cultural characteristics, as well as toxin production, bacteria of the genus Salmonella differ from each other in biochemical and antigenic (serological) properties. These differences form the basis of scientifically developed typing methods.

Typing Methods Salmonella There are two main methods for typing (that is, establishing species) of bacteria of the genus Salmonella: serological and biochemical.

For serological typing, an agglutination reaction with Salmonella sera is used. It is known that the introduction of a foreign protein (antigen) into the body causes the formation of corresponding antibodies in the blood serum of animals. Antigens of Salmonella bacteria are complex in composition. With few exceptions, Salmonella have two types of antigens: heat-stable 0-antigen (somatic, associated with the body of bacteria) and heat-labile H-antigen (flagellar, associated with the locomotor apparatus of bacteria). Each of these antigens consists of two or more components or fractions (receptors). A very complex flagellar antigen is divided into 1-specific and 2-nonspecific phases. In some Salmonella (nonmotile S. pullorum, S. gallinarum) do not have an H-antigen, while others do not have a nonspecific phase of the H-antigen. Such single-phase bacteria include S. paratyphi A, S. derby and many representatives of the serological group D. According to the difference in the structure of O- and H-antigens in certain species of Salmonella Kaufman and White divided bacteria of this genus into several serological groups - A, B, C, D, E, etc. Each type of bacteria included in a specific serological group will agglutinate with serum prepared by immunization of an animal with a culture of any bacteria from this group. Such sera are called group sera, and the agglutination reaction with them is called group sera. A positive agglutination reaction when performed with five group sera (A, B, C, D, E, ib, which includes the most commonly isolated species of Salmonella bacteria from meat) indicates that the bacteria belong to the Salmonella genus. Together with group biofactories, our biofactories prepare specific or monoreceptor serums. To do this, serum obtained by immunizing an animal with bacteria of one type of Salmonella is mixed with a washout of an agar culture of bacteria of another type. The mixture is kept for 2 hours in a thermostat, then 18-20 hours on an icebox, after which it is centrifuged. The clear whey is filtered off. As a result, the serum will be depleted and will contain only one or a few antigen factors.

The monoreceptor serum obtained by immunizing the animal will agglutinate only S. paratyphi B, which has factor b in its H-antigen. If a positive reaction with one of the group sera indicates that the isolated cultures belong to the genus Salmonella and to one or another serological group, then the agglutination reaction with mono-receptor sera makes it possible to type representatives of these bacteria directly to the species.

Biochemical typing is based on the difference in the composition of enzymes in Salmonella. Due to enzymatic (biochemical) differences, some bacteria are able to decompose certain carbohydrates or alcohols, while others do not have this ability. For biochemical typing, elective media (Endo, Smirnova, Levin, Ploskirova, etc.) and a colored (variegated) series of media are used. Each of these media contains two components: an ingredient—sugar or alcohol—and an indicator—a substance whose color change indicates the decomposition of the ingredient. With the help of selective media and media of the small variegated series, it is possible to differentiate salmonella from bacteria of the genus E. coli, etc., and by changing the media of the large, variegated series, the type of salmonella bacteria can be determined.

The motley series includes Hiss media with various sugars and polyhydric alcohols, as well as broth with glycerin (according to Stern), medium with rhamnose (according to Bitter), milk, litmus milk and meat-peptone broth with indicator paper (for hydrogen sulfide). During biochemical typing, in addition to changing the color of the media, the ability of bacteria to form hydrogen sulfide, indole, etc. is studied. The belonging of a culture to a certain type of bacteria based on changes in a variegated series of media is established using tables or determinants that are available in educational manuals for practical exercises in veterinary examination. Consequently, typification of bacteria of the genus Salimonella and determination of their species are possible only as a result of bacteriological research.

Bacteriological research. Meat and meat products are examined according to GOST 21237-75 to detect contamination with bacteria of the genus Salmonella (as well as opportunistic bacteria, staphylococci and anaerobes).

Pathogenicity of bacteria of the genus Salmonella for animals. The pathogenic effect of salmonella, like other pathogenic microorganisms, on animals (as well as on humans) manifests itself when complex mechanisms between micro- and macroorganisms are disrupted. (The degree of pathogenicity of strains depends on the type of Salmonella, the infectious dose, the biological characteristics of the pathogen, as well as the age of the macroorganism, its resistance and other factors. A sufficient amount of data has now accumulated in the literature indicating the inconsistency of distinguishing Salmonella into pathogenic only for humans and animals.

In animals, including birds, under natural conditions, salmonella are causative agents of septic infectious diseases called paratyphoid fever, or salmonellosis. In accordance with pathogenesis and epizootology, these diseases are divided into primary and secondary salimonellosis. In addition, paratyphoid (Salmonella) enteritis of adult cattle is separately distinguished, which may have the nature of a primary or secondary disease, as well as Salmonella carriage in animals.

Primary salmonellosis - Typical infectious diseases that are caused by specific pathogens, during their course, have a certain clinical picture and pronounced pathological changes. Primary salmonellosis includes: salmonellosis (paratyphoid) of calves (pathogens S. dubin, S typhimurium), salmonellosis of piglets (pathogens S typhisuis, S. choleraesuis, less often S. dublin), salmonellosis of lambs (pathogen S. abortusovis), salmonellosis of foals (pathogen S. abortusequi), poultry salmonellosis (pathogen S. typhimurium, less often S. essen, S. anatum), pullorosis-typhoid fever of chickens (pathogen S. qallinarum-pullorum]J

Salmonellosis (paratyphoid) of calves is one of the most common salmonellosis diseases, and in terms of the severity of clinical signs and pathological and anatomical changes, it is classified as “classic”. Calves from 2 weeks to 3-6 months of age, and sometimes even older, are susceptible. The disease, as a rule, has the character of a persistent stall infection and is often acute. Clinically, it manifests itself as weakness, drowsiness and decreased appetite in calves. Body temperature can rise to 41 °C and higher, short-term constipation is replaced by persistent profuse diarrhea, even with an admixture of blood and mucus in the stool. As the disease progresses, rapidly progressive emaciation of calves occurs. Toward the end of the disease, exhaustion, ruffled fur, and sunken eyes into the orbit are observed. In case of prolonged paratyphoid fever, calves develop pneumonia, swelling of the joints occurs, mortality can be 25-30%, and sometimes even up to 60%.

During post-mortem diagnostics, the most characteristic pathological changes are also detected in salmonellosis of calves. These changes are as follows: diffuse catarrhal or catarrhal-hemorrhagic inflammation of the abomasum and intestines, on the mucous membrane of the abomasum and intestines with hemorrhages in them, and lymphatic hyperemia, enlargement of the spleen, hemorrhages on the serous membranes and in the cortical layer of the kidneys. A particularly characteristic sign of salmonellosis in calves is the presence of yellowish-gray necrotic nodules in the liver, which are found both under the serous membrane and on the cut surface of the organ.

Inflammation of the joints with the presence of fibrin flakes in the synovial fluid is often observed. In the lungs, especially in the anterior and middle lobes, dark red pneumonic foci and numerous hepatized areas with small yellowish necrotic foci (pneumonia) are possible. Salmonellosis of calves in some cases is accompanied by yellowness of all tissues. With other salmonellosis, only individual pathological signs are found from the general complex that is revealed during post-mortem examination of the organs of calves sick with salmonellosis. With salmonellosis in pigs, the pathological changes are in many ways similar to those with plague.

Secondary salmonellosis do not represent independent diseases, but occur in animals (including birds) that carry salmonella during infectious, invasive and non-contagious diseases, poisoning and septic-pyemic processes, prolonged fasting, overwork and other factors that reduce the body’s resistance. Under these factors, the virulence of Salmonella increases, they multiply intensively and penetrate from their original localization sites (intestines, liver, mesenteric lymph nodes) into various organs and muscles. In this regard, pathological changes can be very diverse and are largely determined by the primary pathological process on which secondary salmonellosis is superimposed. Hemorrhages in various organs, especially in the liver, kidneys and lymph nodes, hemorrhages on the serous membranes, poor bleeding of carcasses, abscesses in the liver, arthritis, fatty degeneration of the liver give reason to suspect secondary salmonellosis. Secondary salmonella diseases of animals are most often encountered in the practice of veterinary and sanitary examination and play a large role in the occurrence of foodborne toxic infections in humans.

Salmonella (paratyphoid) enteritis in adult cattle is caused by S. enteritidis, S dublin, as well as S. typhimurium and may have the character of a primary or secondary disease. The most characteristic pathological signs of this disease are the following: low fatness of carcasses, hyperemia and hemorrhages on intestinal mucosa, enlargement and blood filling of the spleen with crimson coloration of the pulp, enlargement and fragility of the liver, inflammation of the gallbladder, enlargement and hemorrhagic inflammation of the lymph nodes, sometimes in the liver there are single or grouped typical paratyphoid nodules the size of a poppy seed to a pinhead and icteric staining all fabrics. The final diagnosis of salmonella diseases, as well as salmonella carriage in animals, is made on the basis of bacteriological examination.

Pathogenicity of bacteria of the genus Salmonella for humans. As stated above, Salmonella do not have enterally acting toxins, and their pathogenicity on the human body is manifested by the combined effect of living microbes and toxins. Once in the gastrointestinal tract with meat and other foods, toxic substances sensitize the intestinal mucosa and disrupt its reticuloendothelial barrier. This contributes to the rapid penetration of Salmonella bacteria into the blood and the development of bacteremia. When bacteria are destroyed in the body, endotoxin is released, which largely determines the clinical picture of toxic infection.

Gastroenteric form manifested by increased body temperature, chills, nausea, vomiting, loose stools, sometimes mixed with blood and mucus, abdominal pain, increased thirst and headaches. The disease is especially severe, with symptoms of uncontrollable vomiting and even damage to the nervous system, when S. typhimurium enters the human body with food.

Typhoid-like form may begin with ordinary gastroenteritis and, after an apparent temporary recovery, after a few days it manifests itself with signs characteristic of ordinary typhoid fever.

Flu-like form quite common in human illness, characterized by pain in the joints and muscles, rhinitis, conjunctivitis, catarrh of the upper respiratory tract and possible gastrointestinal disorders.

Septic form occurs in the form of septicemia or septicopyemia. In this form, local septic processes caused by Salmonella are observed with localization of foci in internal organs and tissues: endocarditis, pericarditis, pneumonia, cholecystitis, osteomyelitis, arthritis and abscesses, etc.

The mortality rate for salmonella toxic infections averages 1-2%, but depending on the severity of outbreaks, the age composition of people (disease among children) and other circumstances, it can reach up to 5%. Based on literature data, many authors do not consider it correct to call this disease in humans Salmonella toxicoinfection. In their opinion, recognition of the great pathogenetic significance of toxinemia, which is impossible without a living pathogen, does not provide grounds for calling this disease that way. I. S. Zagaevsky and others consider it more correct to call this disease food-borne salmonellosis.

Epidemiology of food salmonellosis. According to domestic and foreign authors, the leading role in the occurrence of food-borne salmonellosis belongs to meat and meat products. Particularly dangerous in this regard is meat and offal (liver, kidneys, etc.) from forcedly killed animals. Intravital contamination of muscle tissue and organs with Salmonella occurs as a result of animal disease with primary and secondary salmonellosis. Dangerous food products from the point of view of the occurrence of foodborne salmonellosis include minced meat, jellies, brawn, low-grade (separate, table, liver, blood, etc.) sausages, meat and liver pates. When grinding meat into minced meat, the histological structure of the muscle tissue is disrupted, and the leaking meat juice contributes to the dispersion of salmonella throughout the entire mass of minced meat and their rapid reproduction. The same applies to pates. Jellies and brawns contain a lot of gelatin, and low-grade sausages contain a significant amount of connective tissue (pH 7.2-7.3). Under these conditions, Salmonella also develops very quickly. Waterfowl are often salmonella carriers, and therefore their eggs and meat can be a source of foodborne salmonellosis. Less commonly, Tomsk infections are possible when eating milk and dairy products, fish, ice cream, confectionery (cream pastries and cakes), mayonnaise, salads, etc.

Exogenous contamination of meat and prepared foods with Salmonella should also be taken into account. Sources of exogenous contamination can be various environmental objects: water and ice, containers, knives, tables, production equipment, with the help of which primary processing and processing of products is carried out; The participation of biological agents in the contamination of products with Salmonella (mouse-like rodents, flies) is also not excluded. The contact route of infection with salmonella according to the “animal (bacterium-excreting) - human” scheme cannot be excluded. Indoor animals (dogs, cats), as well as pigs, poultry and even pigeons play a certain role in this. Contact factor transmission according to the “person-to-person” scheme is a rare phenomenon and occurs more often in children.

Prevention of food salmonellosis. Through the veterinary service, prevention can be ensured by carrying out the following basic activities.

In livestock farms and specialized complexes, it is necessary to comply with sanitary and hygienic rules and standards for keeping and feeding animals, carry out health measures, including the prevention and control of primary and secondary salmonellosis, prevent on-farm and backyard slaughter of livestock and poultry, and examine the degree of bacterial contamination of animal feed origin (meat and bone, fish meal, etc.), control the milking regime of cows and primary milk processing, etc.

At meat processing plants and slaughterhouses, it is necessary to prevent tired animals, sick and convalescent paratyphoid animals from being slaughtered for meat in a sanitary slaughterhouse, to properly organize pre-mortem inspection of livestock and poultry, post-mortem examination of carcasses and organs and laboratory testing of products. An important condition is compliance with sanitary requirements during technological processes for the slaughter of lambs and poultry, primary processing of carcasses and organs, processing of meat and other food products, as well as compliance with the temperature regime during transportation and storage, since at temperatures above 4 °C Salmonella may develop. It must be borne in mind that salmonella-contaminated meat has no organoleptic signs of staleness, since the bacteria are not proteolytic, but saccharolytic. Toxic infections in people can arise from eating apparently completely fresh meat.

In veterinary health laboratories of markets, it is necessary to conduct a thorough post-mortem veterinary examination of carcasses and organs, veterinary examination of all products of animal and plant origin and control their trade on the market, have refrigerators for storing products sent for bacteriological examination, as well as installations for sterilization of meat subject to disinfection.

Sanitary assessment of products when salmonella is detected. When Salmonella is isolated from the muscle tissue of slaughtered animal carcasses, lymph nodes or internal organs, the internal organs are subject to technical disposal, and the carcasses are disinfected by boiling or sent for processing into meat bread and canned food. This sanitary assessment of meat is carried out regardless of the type of salmonella isolated. Finished food products in which salmonella are found are destroyed.

61. Pathogenic salmonella (causative agents of typhoid fever and paratyphoid fever A, B): taxonomy, morphology, cultural and tinctorial properties, biochemical features, antigenic structure and toxin formation, pathogenesis and clinic. Microbiological diagnostics. Prevention and treatment.

Genus Salmonella.

Salmonella is a large group of enterobacteria, among which various serotypes are the causative agents of typhoid fever, paratyphoid fevers A, B and C and the most common foodborne toxic infections - salmonellosis. Based on their pathogenicity for humans, Salmonella are divided into pathogenic for humans - anthroponoses (cause typhoid fever and paratyphoid A and B) and pathogenic for humans and animals - zoonoses (cause salmonellosis). Despite the significant differences between Salmonella in antigenic characteristics, biochemical properties, and the diseases they cause, according to the modern, but insufficiently convenient and perfect classification, two species are distinguished - S.bongori and S.enteritica. The latter is divided into subspecies, of which the subspecies choleraesuis and salamae are the most important. The subspecies choleraesuis contains the largest proportion of known Salmonella serovars (about 1400 of about 2400).

Morphology. Straight gram-negative rods measuring 2-4 x 0.5 µm. Motile due to the presence of peritrichial flagella.

Cultural and biochemical properties. Facultative anaerobes, grow well on simple nutrient media. Optimum pH - 7.2-7.4, temperature - +37. Metabolism - oxidative and fermentative. Salmonella ferment glucose and other carbohydrates to produce acid and gas (the Salmonella typhi serotype does not cause gas formation). Usually lactose (on media with this carbohydrate - colorless colonies) and sucrose are not fermented. Oxidase is negative, catalase is positive. The Voges-Proskauer reaction is negative.

Based on their biochemical (enzymatic) properties, Salmonella are divided into four groups. Characteristic signs of Salmonella are the formation of hydrogen sulfide, lack of indole production and aerobic activity. For isolation, differential diagnostic media (bismuth - sulfite agar, Endo, Ploskirev, SS agar) and enrichment media (selenite broth, bile broth, Rappoport medium) are used. S-forms form small (from 1 to 4 mm) transparent colonies (on Endo medium - pinkish, on Ploskirev medium - colorless, on bismuth - sulfite agar - black, with a metallic sheen). In liquid media, S-forms give uniform turbidity, R-forms give a sediment.

Antigenic structure. O-, H- and K-antigens are isolated. The group of K-antigens includes Vi-antigens (virulence antigens). Due to its more superficial location (than O-antigens), Vi-antigen can prevent agglutination of Salmonella cultures with O-specific serum (shielding). To differentiate Salmonella, the Kaufmann-White scheme (serological classification) is used.

In accordance with the structure of O-antigens, Salmonella are divided into O-groups (67 serogroups), each of which includes serological types that differ in the structure of H-antigens. The belonging of Salmonella to a specific serovar is established by studying the antigenic structure in accordance with the Kaufmann-White scheme. Examples: serotype S.paratyphi A belongs to serogroup A, S.paratyphi B belongs to serogroup B, S.paratyphi C belongs to group C, S.typhi belongs to serogroup D.

Pathogenicity factors.

1.Adhesion and colonization factors.

3.Endotoxin (LPS).

4. Heat-labile and heat-stable enterotoxins.

5. Cytotoxins.

6. Virulence plasmids and R-plasmids are essential.

7. Vi - antigen inhibits the action of serum and phagocytic bactericidal factors.

The main factors of the pathogenicity of Salmonella are their ability to penetrate macrophages and multiply in the lymphoid formations of the mucous layer of the small intestine (Peyer's patches, solitary follicles), as well as the production of endotoxin.

Pathogenesis of lesions. The differences in clinical forms of diseases caused by Salmonella depend on the virulence and dose of the pathogen and the state of the body's immune system. The usual dose that causes clinical manifestations is 106 - 109 bacteria; a smaller dose is sufficient for immunodeficiencies, hypochlorhydria and other diseases of the gastrointestinal tract.

The following main forms of salmonella infection are distinguished:

Gastrointestinal;

Generalized (typhoid-like and septicopyemic variants);

Bacterial carriage (acute, chronic, transient).

Significant pathogenetic features of the infectious process caused by serotypes S.typhi, S.paratyphi A,B are the basis for classifying typhoid paratyphoid diseases into an independent nosological group. Each phase of pathogenesis corresponds to a clinical period of the disease and its own laboratory examination tactics. The main phases are the introduction of the pathogen (corresponding to the incubation period), primary localization of the pathogen (prodromal period), bacteremia (first week of the disease), secondary localization of Salmonella (the height of the disease - 2-3 weeks), excretory-allergic (reconvalescence - 4 weeks of the disease).

Salmonella entering through the mouth enters the epithelial cells of the duodenum and small intestine through endocytosis. They easily penetrate epithelial cells, but do not multiply here, but pass and multiply in the lymphatic apparatus of the small intestine. Salmonella multiply predominantly in the lamina propria (primary localization), which is accompanied by a local inflammatory reaction of the mucous membrane, an influx of fluid into the lesion and the development of diarrhea syndrome (gastroenteritis). Enterotoxins increase the level of cyclic adenomonophosphate (cAMP), an increase in the level of histamine and other biologically active substances, and vascular permeability. Water and electrolyte disturbances are observed, hypoxia and acidosis develop, which aggravate the pathological process with a predominance of vascular disorders. Some Salmonella are destroyed with the release of endotoxin and sensitization (HRT) of the lymphatic apparatus of the small intestine occurs.

From the mucous membrane, salmonella can enter the lymph and then into the bloodstream, causing bacteremia. In most cases, it is transient in nature, because Salmonella are eliminated by phagocytes.

Unlike other salmonella, the causative agents of typhoid and paratyphoid fever, having penetrated the bloodstream, are able to survive and multiply in phagocytes. They can multiply in the mesenteric lymph nodes, liver and spleen and cause generalization of the process. After the death of phagocytes, Salmonella enters the blood again. In this case, Vi-antigen inhibits bactericidal factors.

When salmonella die, endotoxin is released, which inhibits the activity of the central nervous system (typhoid - from the Greek typhos - fog, confusion) and causes prolonged fever. The action of endotoxin can cause myocarditis, myocardial dystrophy, and infectious and toxic shock.

As a result of bacteremia, generalized infection of the gallbladder, kidneys, liver, bone marrow, and dura maters occurs (secondary localization of Salmonella). Secondary invasion of the intestinal epithelium, especially Peyer's patches, occurs. In the wall sensitized by salmonella, allergic inflammation develops with the formation of the main dangerous complication - typhoid ulcers. Long-term carriage of Salmonella in the gallbladder is observed with the release of the pathogen in feces, pyelonephritis, bleeding and intestinal perforation when Peyer's patches are affected. Then the formation of post-infectious immunity occurs, elimination of the pathogen and healing of ulcers or the formation of bacterial carriage (in Western Siberia, often against the background of chronic opisthorchiasis).

The causative agents of salmonellosis are other serotypes of salmonella that are pathogenic for humans and animals (S.typhimurium, S.enteritidis, S.heldelberg, S. newport and others). The pathogenesis of salmonellosis is based on the action of the pathogen itself (its interaction with the host body) and endotoxin that accumulates in food products infected with salmonella. In the classic version, Salmonella toxicoinfection is gastroenteritis. However, when the intestinal lymphatic barrier breaks, generalized and extraintestinal forms of salmonellosis can develop (meningitis, pleurisy, endocarditis, arthritis, liver and spleen abscesses, pyelonephritis, etc.). The increase in generalized and extraintestinal forms of salmonellosis is associated with an increase in the number of immunodeficiency states, which is of particular importance in HIV infection.

A separate problem is posed by hospital strains of Salmonella (usually individual phages of S.typhimurium), which cause outbreaks of nosocomial infections mainly among newborns and weakened children. They are transmitted mainly through contact and household contact from sick children and bacteria carriers; they are highly invasive, often causing bacteremia and sepsis. Epidemic strains are characterized by multiple drug resistance (R-plasmids), high resistance, including to high temperatures.

Epidemiological features. Characterized by widespread distribution. The main reservoirs of salmonella are humans (causative agents of typhoid fever and paratyphoid A) and various animals (other serotypes of salmonella). The main pathogens are polypathogenic. The main sources of infection are meat and dairy products, eggs, poultry and fish products. The main routes of transmission are food and water, less often - contact. Characterized by an extreme multiplicity of reservoirs and possible sources of infection. Farm animals and birds are of primary importance.

Laboratory diagnostics. The main method is bacteriological. Based on the pathogenesis, the optimal time for bacteriological studies for gastrointestinal forms is the first days, for generalized forms - the end of the second - the beginning of the third week of the disease. When examining various materials (stool, blood, urine, bile, vomit, food debris), the highest frequency of positive results is observed in the study of feces; for the causative agent of typhoid fever and paratyphoid fever - blood (blood culture).

Research is carried out according to a standard scheme. The test material is inoculated on dense differential diagnostic media - highly selective (bismuth sulfite agar, brilliant green agar), medium selective (Ploskirev's medium, weakly alkaline agar), low selective (Endo and Levin agars) and in enrichment media. Rapoport medium is used for blood culture. On bismuth-sulfite agar, Salmonella colonies acquire a black (rarely greenish) color. The grown colonies are subcultured onto media for primary (Russell's medium) and biochemical (hydrogen sulfide, urea, glucose, lactose) identification. For preliminary identification, the O1-salmonella phage is used, to which up to 98% of salmonella are sensitive.

To identify cultures in RA, polyvalent and monovalent O-, H- and Vi-antisera are used. First, polyvalent adsorbed O- and H-sera are used, and then the corresponding monovalent O- and H-sera are used. To identify the causative agents of typhoid fever and paratyphoid fever, antibodies to the O2 (S.paratyphi A), O4 (S.paratyphi B), O9 (S.typhi) antigen are used. If the culture is not agglutinated by O-serum, it should be examined with Vi-serum. To quickly detect Salmonella, polyvalent luminescent sera are used.

Serological studies are carried out for diagnosis, as well as identification and differentiation of various forms of carriage. RA (Widal reaction) is used with O- and H-diagnosticums and RPGA using polyvalent erythrocyte diagnosticums containing polysaccharide antigens of serogroups A, B, C, D and E and Vi-antigen.

Treatment is antibiotics (chloramphenicol, etc.). Antibiotic-resistant strains are often identified. It is necessary to determine the antibiotic resistance of isolated cultures.

Specific prophylaxis can be used primarily for typhoid fever. A chemical sorbed typhoid monovaccine is used. Vaccination is currently used mainly for epidemic indications.