Yersinia properties. The causative agent of yersiniosis
81. Pathogenic Yersinia (pathogens of plague, pseudotuberculosis and intestinal yersiniosis): taxonomy, morphology, cultural and tinctorial properties, biochemical features, antigenic structure and toxin formation, pathogenesis and clinic. Microbiological diagnostics. Prevention and treatment.
Genus Yersinia.
The genus includes 11 species. Y. pestis causes plague, Y. pseudotuberculesis - pseudotuberculosis, Y. enterocolitica - (intestinal) yersiniosis, a number of species are not pathogenic or opportunistic for humans.
Morphology.
More often they have an ovoid (cocco-bacillary) form, are stained bipolarly, and are prone to polymorphism. Most species are motile at temperatures below +30 degrees Celsius (have peritrichous flagella), are gram-negative, and have a capsular substance. Y.pestis are nonmotile and have a capsule.
Cultural and biochemical properties.
Facultative anaerobes. Temperature optimum is from +25 to + 28 degrees Celsius, pH is close to neutral. They grow well on simple nutrient media. Most carbohydrates are fermented without producing gas. Yersinia is able to change its metabolism depending on temperature and reproduce at low temperatures (psychrophilic properties). Virulent strains form rough (R) colonies, transitional (RS) and grayish mucous smooth (S) forms.
When studying colonies of the plague microbe, two types of colonies are distinguished - young and mature. Young microcolonies with jagged edges (the “broken glass” stage) subsequently merge, forming delicate flat formations with scalloped edges (the “lace handkerchief” stage). Mature colonies are large, with a brown granular center and jagged edges (“daisies”). Many strains are capable of reducing dyes that have discolored media (methylene blue, indigo, etc.). On slanted agar, after two days at +28 C, a grayish-white coating forms, growing into the medium; on broth, a delicate surface film and a cotton-like sediment form. Temperature +37C is selective for capsule formation in Y.pestis.
Cultures of Y.pseudotuberculosis and Y.enterocolitica do not have the “broken glass” stage; at first they are small, shiny, convex, then confluent growth can be observed with the formation of convex, tuberous colonies, similar to Y.pestis colonies. They grow on universal nutrient media (Endo medium, Mac Conkey agar, Serov medium, etc.) in combination with accumulation methods in cold conditions.
Antigenic structure.
All types of Yersinia have an O - antigen (endotoxin), similar to the O - antigens of other gram-negative bacteria and toxic to humans and animals. Lipopolysaccharide-protein complexes of O - antigens of Yersinia are divided into S (smooth) and R (rough), the latter being common to Y. pestis and Y. pseudotuberculosis. Y. enterocolitica has a surface antigen that is common to other enterobacteria.
The causative agent of pseudotuberculosis by O- and H-antigens is divided into 13 serovars, serovar I, as well as III and IV are more common, yersiniosis is divided into 34 serovars by O-antigen, serovars O3 and O9 are most often isolated from humans. At temperatures from +22 to +25C, Y.pseudotuberculosis and Y.enterocolitica have flagellar antigen and are motile; at +37C they lose H - antigen and motility.
Y. pestis is more homogeneous antigenically, having a capsular antigen (fraction I), antigens T, V - W, plasmacoagulase proteins, fibrinolysin, outer membrane, etc. The plague microbe secretes bacteriocins (pesticins), which have a bactericidal effect on the pseudotuberculosis microbe and strains coli.
Pathogenic properties.
The causative agent of plague has the greatest pathogenic potential among bacteria. It suppresses the functions of the phagocytic system, since it suppresses the oxidative burst in phagocytes and multiplies unhindered in them. Pathogenicity factors are controlled by three classes of plasmids. In pathogenesis, there are three main stages - lymphogenous introduction, bacteremia, generalized septicemia.
The causative agents of pseudotuberculosis and yersiniosis have adhesins and invasins, low molecular weight proteins (inhibit bactericidal factors), and enterotoxin. Some factors are controlled by virulence plasmids.
Clinical features.
Plague most often occurs in bubonic, pneumonic and intestinal forms. The most dangerous are patients with pneumonic plague, who secrete huge amounts of the pathogen in their sputum).
Yersiniosis and pseudotuberculosis are intestinal infections. The clinical picture is varied - regional lymphadenopathy (imitates appendicitis), enterocolitis, reactive arthritis, ankylosing spondylitis, scarlet fever.
Epidemiological features.
Plague is a classic natural focal zoonosis of wild animals. The main carriers in nature are marmots, gophers, gerbils, pikas, and in anthropourgic (urban) conditions - rats (the plague of port cities). In the transmission of the pathogen, especially in areas where non-hibernating animals predominate, animal fleas are capable of attacking and infecting humans. Camels can become infected in sand outbreaks and pose an epidemic risk.
Pseudotuberculosis and intestinal yersiniosis are transmitted in nature by rodents. They can be stored for a long time and even accumulate at low temperatures, for example, in vegetable stores. Capable of causing diseases in farm animals. They are transmitted to humans mainly through food products from animals, as well as plant origin.
Laboratory diagnostics.
Bacteriological diagnosis of plague can only be carried out by specialized laboratories of anti-plague stations and institutes (pathogenicity group 1). Methods for express antigen detection are MFA, RPGA with erythrocyte diagnosticum, sensitized with monoclonal antibodies to the capsular antigen, ELISA, RNAT. For serological diagnosis, ELISA, RNAG, ELISA can be used.
In the bacteriological diagnosis of intestinal yersiniosis and pseudotuberculosis, due to the accumulation of the pathogen at low temperatures (unlike most other microorganisms), the material is first taken into a buffered saline solution and stored in the refrigerator with periodic seeding on Endo, Ploskirev, Serov media. Suspicious colonies are subcultured to obtain pure cultures, studied by their biochemical properties and identified in RA with diagnostic sera.
For serological diagnosis, RA and RNGA are used (for pseudotuberculosis - with serovar I, for yersiniosis - with serovars O3 and O9) with the study of paired sera taken in the dynamics of the infectious process.
Specific prevention.
Used in plague outbreaks. A live attenuated vaccine from the EV strain is used. There is a dry tablet vaccine for oral use. To assess immunity to plague (natural post-infectious and vaccine), an intradermal allergy test with pestin can be used.
5. Yersinia
The genus Yersinia contains seven species, of which pathogenic for humans are Y. pestis (the causative agent of plague), Y. pseudotuberculesis (the causative agent of pseudotuberculosis), Y. enterocolitica - the causative agent of acute intestinal infections, intestinal yersiniosis.
Y. enterocolitica are gram-negative motile rods that do not form spores or capsules. They are cultivated on simple nutrient media at a temperature of 20–26 °C.
Biochemical properties:
1) ferment sorbose and inositol to form acid;
2) form urease.
Based on their specificity, O-antigens are divided into 30 serovars. The disease is most often caused by serovars O3 and O9.
Yersinia is resistant and capable of reproduction in external environment, withstand low temperatures. Capable of multiplying in milk, vegetables, fruits, ice cream at low temperatures. In open waters they survive and reproduce.
Yersiniosis is a zooanthroponotic disease. The reservoir is a variety of rodents that excrete bacteria in feces and urine. The route of infection is nutritional. Diseases are recorded as outbreaks or sporadic cases.
Infection can manifest itself in different ways: from asymptomatic carriage and mild forms to severe and generalized, septic (more often in the elderly, suffering chronic diseases).
There are four phases in pathogenesis.
1. Implementation. Yersinia has tropism for epithelial cells small intestine, penetrate the lymphatic system.
2. Enteral. Reproduction is accompanied by the death of microorganisms and the release of endotoxin. Clinically expressed by the phenomena of enterocolitis and lymphadenitis. At this stage, the process may end, then a typical intestinal infection develops. If a breakthrough of the lymphatic barrier occurs, then the third phase follows.
3. Bacteremia: sepsis and scarlet fever develop.
4. Secondary focal and allergic manifestations. Hepatitis, arthritis, and urticaria are recorded. Any organs may be affected.
Cseudotuberculosis and yersiniosis are acute bacterial infectious diseases from the group of alimentary zoonoses, characterized by general intoxication, frequent development of gastroenterocolitis, polymorphism of clinical manifestations, a tendency to generalize the process with the development of lesions of various organs and systems, recurrent and protracted course.
Prevalence. The first reports about the causative agent of pseudotuberculosis date back to the end of the 19th century, but the systematic study of it as a human disease with a certain clinical characteristic began in 1953, when W. Maschoff, W. Knapp (1954) isolated the disease from the group of non-tuberculous mesenteric lymphadenitis , having a distinct morphological characteristic, the cause of which turned out to be these bacteria. A disease affecting the mesenteric lymph nodes, mainly in children and adolescents, was registered in these years in the USSR [Yushchenko G.V. et al., 1964]. In subsequent years Far East with etiological unknown disease, called “Far Eastern scarlet-like fever,” the causative agent of pseudotuberculosis was isolated, which served as an impetus for an in-depth study of this disease.
The causative agent of yersiniosis was isolated in the 40s of the current century, but was not classified as an independent species. Only in the 60s, after the appearance of these bacteria in humans with clinical manifestations of appendicitis, hepatitis, sepsis, as well as their isolation from various animals, their independence was established, and the disease they caused was defined as a new nosological form. In subsequent years, it was proven that in terms of severity, frequency of occurrence and nature of morbidity, pseudotuberculosis and yersiniosis are no less significant than salmonellosis and other food zoonoses.
Yersiniosis is currently registered in all countries of the world, regardless of climate zone, but the incidence rate varies sharply in different countries. It is significantly higher in countries with a high economic level and a developed food industry, where food outbreaks have been described along with isolated cases. In the USSR, sporadic cases of yersiniosis have been identified in almost all climatic zones - beyond the Arctic Circle and in republics with a hot and dry climate. Outbreaks have been recorded primarily in large cities.
Outbreaks of pseudotuberculosis are observed mainly in the USSR. In other countries of the world, including European ones, as well as in Canada and Japan, sporadic cases have been reported. In the USSR, this infection is detected mainly in areas with a temperate climate and fairly high humidity, while sporadic cases have been identified in the southern regions (Uzbekistan, Georgia, Azerbaijan).
In various environmental objects, in rodents and farm animals, the causative agents of yersiniosis and pseudotuberculosis are detected in almost all territories.
Consequently, Y. pseudotuberculosis and especially Y. enterocolitica have a ubiquarian distribution, but for the manifestation of morbidity a certain complex of social
environmental conditions, which determines the nature of the incidence of these infections.
Etiology. Y. pseudotuberculosis and Y. enterocolitica are included in the genus Yersinia, which is part of the family of enterobacteria [Yushchenko G.
V., 1985J. The causative agents of pseudotuberculosis and yersiniosis are largely similar to each other. These are rod-shaped bacteria with rounded ends, 0.8-1.5 nm long, 0.5-1.0 nm wide. The size of the rods may vary depending on the conditions of their cultivation. They are larger and longer when grown at temperatures up to 22-25°C and short coccoid when grown at 37°C.
Microorganisms are dyed with all aniline dyes. They can stain bipolarly, which is better detected in smears from broth cultures or in preparations from the organs of animals that died from pseudotuberculosis. Do not stain for Gram
Bacteria are motile at temperatures no higher than 25° C. Motility is expressed in Y. enterocolitica. It is provided by flagella. In the causative agent of pseudotuberculosis there are few of them and they are located extrapolarly, in Yersinia enterocolitica the flagellar apparatus is well developed, the flagella are located peritrichially. In addition to flagella, both types of bacteria have fimbriae, which are located over the entire surface and can exceed the size of the cell body in length. Bacteria do not have spores. Under certain cultivation conditions, a capsule substance is formed. Yersinia is unpretentious and undemanding to nutrients; it is easily cultivated in ordinary nutrient media - slightly alkaline and elective. The optimal pH for cultivation is in the range of 7.2-7.4.
The most favorable temperature for growth is considered to be from 22 to 28° C. Due to their ability to grow at lower temperatures, they are classified as psychrophiles. They grow well at temperatures of 30-37° C, but under these conditions dissociation and transition to the R-form are observed. When cultivated in slightly alkaline media at a temperature of 22-25 ° C for 18-20 hours, colonies with a diameter of up to 0.1-0.2 mm grow. They are convex, translucent with a smooth edge. Some colonies may have a bay-shaped edge and a striated surface. At a temperature of 37° C, colonies of the causative agent of pseudotuberculosis have an uneven, thinned edge, a convex, bumpy or striated center (SR- and S-forms), colonies of the causative agent of yersiniosis are usually smoother with a bay-shaped edge outlined by the center.
The causative agents of pseudotuberculosis and yersiniosis do not produce hydrogen sulfide, emit ammonia, have the ability to reduce nitrates into nitrites, do not have fibrinolytic, plasma-coagulating proteolytic enzymes. Both types ferment to acid without gas: arabinose, glucose, mannose, maltose, glycerol, mannitol, inositol. Do not ferment: lactose, inulin, sorbitol, dulcite, amygdalin, produce catalase and p-galactosidase. They also utilize urea, do not form oxidase, phenylalanyl deaminase, lysine decarboxylase, and give a positive reaction to methylrot. These types of bacteria differ from each other in rhamnose, sucrose, cellobiose, sorbitol, adonite, ornithine decarboxylase, indole. Biovars in the causative agents of pseudotuberculosis have not been identified. At the same time, there is a difference between the strains of serovars I and III. Y.enterocolitica is biochemically heterogeneous and has 5 biovars, differing in a set of biochemical tests (trehalose, xylose, indole, esculin, salicin, lecithinase).
According to the O-antigen, the causative agents of pseudotuberculosis have six serovars (I-VI). The most common strains that cause disease in humans and animals all over the world are serovore I strains (up to 90%); in second place is serovar III (up to 10%), then IV (up to 1%); diseases associated with serovars II, V and VI are rare.
The causative agent of yersiniosis has a more complex scheme, including 30 serogroups. The most epidemiologically significant strains are serovars 0:3; 0:9; 0:5; 27; 0:8.
The causative agent of pseudotuberculosis is mainly resistant to penicillin. There are reports of weak sensitivity of some strains to this antibiotic. Y. enterocolitica is resistant to this antibiotic. Both species are sensitive to gentamicin, streptomycin and other aminoglycoside drugs, as well as chloramphenicol and tetracycline. In different areas of the country, there are differences in the sensitivity of strains to different antibiotics, which determines the need to study them according to these characteristics.
The serotype, biovar affiliation of Yersinia and, to a lesser extent, the characteristics of sensitivity to antibiotics serve as markers when studying the epidemiological patterns of these infections.
The antigenic structure of bacterial cells is complex and consists of surface and deep components. Surface structures include flagellar, fimbrial, capsular substances and extracellular proteins that determine antigenic complexes of different compositions that have toxic properties. These antigens are found in the cell environment. Both types of pathogens have V and W antigens, which are detected in virulent strains. A heat-stable enterotoxin was identified in Y. pseudotuberculosis and Y. enterocolitica strains. Yersinia contains high molecular weight proteins of lipopolysaccharide nature. In combination with various proteins, lipids and polysaccharides, they form the cell wall and membrane. They also form a complex complex - somatic antigen (O-antigen) - cell endotoxin.
Thus, Yersinia, having a large number of antigens of different nature, which are highly active biological substances, can have various damaging effects on the cells and tissues of a living organism.
The causative agent of pseudotuberculosis is pathogenic for many species of animals and birds. The virulence of different strains varies widely. Along with strains that are highly virulent for white mice (LD-12.6), strains with low virulence (LD-31,400,000) circulate in nature. Y. enterocolitica strains are more heterogeneous in virulence: most strains of these bacteria are practically non-pathogenic for white mice and other laboratory animals.
Both pathogens are unstable to high temperatures. Boiling at a temperature of 100 ° C leads to death within 30-40 s. When heated to 60-80°C, microbes can survive for up to 15-20 minutes. More resistant to cold. They tolerate temperatures well - 15-20°C. These conditions can persist for a long time. They survive at temperatures of -30° C and even -70° C. At temperatures from 4 to 10° C they reproduce, but their growth rate is very weak. They grow well and quickly at temperatures of 15-28° C. They tolerate table salt concentrations of up to 4%, and Y. enterocolitica can grow at 5% or more. The pH range of the environment at which they can exist is significant. They reproduce and survive at a pH of 5 to 8. sun rays have a detrimental effect on both microbes. In direct sunlight they die within a few minutes. They die quickly when they dry out. Disinfectant solutions containing chlorine in conventional formulations kill bacteria within a few minutes. In carbolic acid at the concentrations used in practice, they can remain viable for up to 5-10 minutes.
Consequently, Y. pseudotuberculosiss and Y. enterocohtica belong to psychrophilic, unpretentious bacteria with a wide range of adaptive properties [Somov G. P., 1979]. Capable of existing for a long time in various environmental objects. This determines their epidemiological significance, since, falling into various food products(vegetables, milk, meat), they multiply in them, releasing metabolic products, including toxic ones, which leads to the formation of transmission factors.
Source of the infectious agent. The main sources of infectious agents are animals and birds. Yersinia pseudotuberculosis and especially enterocolitica are widespread among warm-blooded animals.
To date, natural susceptibility to pseudotuberculosis and yersinia microbes has been observed in animals of many species. In the class of mammals, pathogens have been isolated from rodents, insectivores, shrews, carnivores, equids, artiodactyls and monkeys; in the class of birds - from many species, both wild and synanthropic. However, the role of various animals as sources of infectious agents is unequal. Infecting humans through direct contact with rodents (especially wild ones) is almost impossible. A sick pet cared for by a person can be a source of infection, but such cases are rare (from a sick cat and domestic songbirds - with pseudotuberculosis and from a sick puppy of a stray dog - with yersiniosis). Farm animals can be a source of infectious agents for the people caring for them. This is observed with yersiniosis more often when caring for sick pigs that get sick and die from this infection.
Despite the long-term isolation of pathogens from convalescents, the presence of mild and erased forms and carriage in practically healthy people (with yersiniosis), the question of the role of humans as a source of infectious agents has not been completely resolved. As a rule, there are no subsequent diseases in the environment of patients with pseudotuberculosis. At the same time, in catering units, especially when the epidemiological situation becomes more complicated, a significant percentage of infected people are detected (up to 15%). These include patients with mild and incompatible forms, in whom the pathogen is excreted in urine, feces, and less often found in the throat, carriers and practically healthy people, in whom microbial contamination of hands and work clothes is detected. All this does not exclude the role of humans in the formation of the outbreak. With yersiniosis, sequential infection is limited to people who have close contact with the patient (mother - child, children in the same family). There is nosocomial spread of yersiniosis. Patients who actively communicate with each other are more often infected.
The role of vectors (ticks, fleas) in the transmission of pathogens of pseudotuberculosis and yersiniosis has not been established. In the experiment, transmission of pseudotuberculosis pathogens through the bite of carriers was not observed; however, they secrete pathogens for a long time in excrement, infecting environment. Transmission of yersiniosis pathogens through vectors in artificial conditions was not observed. Taking into account the pathogenesis of these infections, the vector-borne route of transmission does not appear to be of significant importance.
Consequently, a feature of pseudotuberculosis and yersiniosis as natural focal infections is the fecal-oral mechanism of transmission of pathogens, which determines natural foci as little dangerous to humans. In natural foci there is a natural circulation of Yersinia along the chain rodent - environment - rodent.
In urban conditions, anthropogenic foci of pseudotuberculosis and yersiniosis are formed in the population of rodents living on their territory. The causative agents of pseudotuberculosis and yersiniosis are constantly found in synanthropic species (grey rats, house mice), much more often in semi-synanthropic species (common voles, field mice) that inhabit the outskirts of cities and, to a lesser extent, in wild ones living in open habitats, sometimes geographically associated with natural.
Infection in the rodent population is recorded throughout the city, and on the outskirts it is 3-5 times more common than in the center. The latter is associated with the peripheral location of objects in which rodents are most affected by pseudotuberculosis. Vegetable storage areas are especially unfavorable for pseudotuberculosis, where there is a fairly high incidence of yersiniosis and pseudotuberculosis in house mice and common voles. Isolation of the pseudotuberculosis microbe from rodents is recorded throughout the year with a significant increase in cases in cold weather, mainly in winter and spring. Just as in a natural outbreak, the spread of the infectious agent within the rodent population occurs mainly through nutrition. Rodents, patients or carriers, releasing pathogens into the environment with feces and urine, contaminate various environmental objects, which causes infection of domestic animals and birds, which become additional reservoirs of the infectious agent.
Despite the fact that the more ancient foci are undoubtedly natural, and anthropogenic foci formed in much more late dates, the latter are more active in epizootological terms due to the high concentration of rodents and, consequently, a more pronounced population density and frequency of their contacts. Intensive contamination of the environment, primarily food products, makes these outbreaks dangerous from an epidemiological point of view, i.e., humans can become involved in the Yersinia circulation chain.
IN rural areas In industrial livestock farms, foci of yersiniosis and, much less often, pseudotuberculosis form. Among farm animals, cows, pigs, sheep, goats, and deer suffer from yersiniosis. These pathogens have been identified in broiler chicken farms.
Yersiniosis in animals, along with carriage, manifests itself in a pronounced clinical picture- diarrhea, miscarriages, mastitis, accompanied by bacteremia and the introduction of pathogens into internal organs, which increases their epidemiological significance.
Findings of Yersinia on various implements, equipment, walls, and in the feed of livestock complexes and poultry farms indicate the continuous circulation of bacteria involving both animals and environmental objects in the chain. The circulation of Yersinia in livestock complexes and poultry farms involves mouse-like rodents that have connections with natural or anthropogenic foci.
Vegetables are grown in natural and rural areas. The possibility of infection cannot be ruled out in the area of natural foci, where the soil can be infected by rodents, farm animal manure used for fertilizer, and water from small reservoirs used for irrigation; Vegetables grown in greenhouses are also seeded. This forms a stable rural focus, from which there is an abundant release of Yersinia into the natural environment with wastewater and manure and the supply of food products contaminated with Yersinia to the population of cities and rural settlements. It has been established that Y. enterocolitica and Y. pseudotuberculosis can be contaminated in various livestock foods and vegetables.
At all stages of the technological process from the cow to the consumer, Y. enterocolitica and, to a lesser extent, Y. pseudotubercuiosis can enter milk, both from a cow suffering from yersinia mastitis and from contaminated containers and equipment. In the finished packaged product, the contamination level reaches 3.7-6.2%.
Significant contamination of meat products. About 5% of meat samples from meat processing plants contain Y. enterocolitica and 1% Y. pseudotuberculosis. They are sown from finished meat products in meat processing plants, from meat and especially offal in sanitary slaughterhouses, from meat and products made from it in stores. Both types of Yersinia were also detected in chicken carcasses (12 and 1.8%, respectively) from eggs and products prepared from them, and containers (up to 2%).
Vegetables, especially those stored for storage, are the most contaminated with Yersinia. When kept in vegetable stores for a long time, they are subject to spoilage, while favorable conditions are created for the existence and reproduction of the pathogen (the presence of a nutrient substrate, humidity and appropriate temperature). Microorganisms accumulate on vegetables and in the environment (equipment, containers, chambers where vegetables are stored, floors, shelves, etc.). At the end of winter and spring, the frequency of detection of Yersinia in vegetables (potatoes, carrots, cabbage, onions) reaches 10-20%. During this period, fruits were also contaminated - apples, citrus fruits up to 9%. Inventory, equipment, containers, floors, shelves, etc. are contaminated (9.8%), including barrels with pickles, scoops and various containers for sauerkraut. Vegetable storage facilities become a huge, long-lasting artificial reservoir of pathogens of yersiniosis and pseudotuberculosis. Contamination of vegetable storage equipment and the environment can persist until the next harvest, which also contributes to the “explosion” of pathogen reproduction in winter and spring and infection of a variety of vegetables placed in them at any time.
Conditions for the seeding of vegetables are created not only in large basic vegetable storage facilities, but also in small warehouses in food departments.
An unfavorable situation with regard to contamination of soil, water and products was revealed in greenhouses (up to 5.3%). Products from greenhouses are sold primarily through vegetable warehouses, where additional pathogens multiply.
Consequently, all types of vegetables and fruits, regardless of their production method and location, are contaminated with both Y. enterocolitica and Y. pseudotuberculosis.
Thus, the existence and spread of Yersinia in the external environment is environmentally determined and is a consequence of the interaction of natural and anthropogenic foci of infection, providing a closed chain of circulation of microorganisms. At the same time, the main source of infectious agents is farm animals and birds, and the leading factor of transmission is food products. Contaminated food products enter households and businesses catering, V including in organized teams.
The introduction of the causative agent of pseudotuberculosis into catering units occurs with any food product (milk, chicken, eggs) and various containers, but vegetables pose the greatest potential danger. Contamination of catering units is detected throughout the year, but during the seasonal rise, the incidence can reach 9%. Violation of sanitary standards for the operation of catering units leads to contamination of premises and equipment both for primary processing of products and for others. During an outbreak, the pathogen is inoculated from dishes, cutting boards, overalls and personnel's hands, tableware, etc. Any other products can become contaminated again through infected equipment and dishes.
Mechanism of transmission of the infectious agent. Pseudotuberculosis and yersiniosis are infections, the main mechanism of transmission of which is fecal-oral, and the food route. This path is the main and leading one. The emergence of group diseases is associated with it.
Transmission of pathogens from a sick animal to a person is possible if sanitary and hygienic rules for working with them are violated. This route is not the main one and does not exclude other mechanisms of infection. It is sold mainly among people involved in livestock farming.
There is a household route of transmission of pathogens, which is possible in family and hospital settings, and is not excluded in food units through infected hands and work clothes, but it is also not the leading one.
Increasing infection of the environment, including the waters of rivers, lakes and other bodies of water, does not exclude the possibility of intensifying water transmission. The aerogenic route of transmission is unknown.
Therefore, infection mainly occurs through consumption of contaminated foods. In yersiniosis, transmission factors are milk, meat and vegetables. In pseudotuberculosis, the leading role as a transmission factor belongs to vegetables eaten without heat treatment. Insufficient cleaning of carrots, radishes, herbs, cucumbers, tomatoes, lack of repeated rinsing when preparing salads and then storing the finished dish in refrigerators create conditions for the accumulation of Yersinia and the products of their metabolism. The same thing happens when microorganisms get into other prepared dishes (compotes, main courses, cottage cheese, sour cream, etc.).
Transmission factors can less commonly be baked goods (crackers, cookies, etc.) and confectionery, contaminated with secretions of rodents, as well as fruits - apples, oranges, tangerines, consumed poorly washed, infected both by rodents and by other means during storage in warehouses.
Population sensitivity. People suffer from yersiniosis and pseudotuberculosis of different ages. The incidence of yersiniosis is registered in children from 2-3 months, pseudotuberculosis - from 6 months to 1 year. Among the cases, children of preschool and school age predominate. The incidence of the disease is high in young people aged 17-20, which is determined by the fact that people of this age often unite in groups. There were no differences in the incidence of men and women.
Contingents who have constant contact with farm animals have a greater risk of infection with yersinia. Among them, the incidence of yersinia is predominantly recorded. A significant percentage (30-40%) of immunopositive individuals was identified in practically healthy workers of various livestock farms.
Most people suffer from pseudotuberculosis urban population and much less often - rural. This is mainly due to the predominance of public catering in cities. With the development in rural areas of conditions closer to urban ones, a tendency towards an increase in morbidity has emerged.
Manifest and severe forms of the disease occur mainly in children with a premorbid background, weakened, and with reduced immunity. In practically healthy individuals, the infectious process is often asymptomatic, causing an immune response, and is accompanied by an increase in the level of specific antibodies in the blood serum.
Immunity to these infections is formed according to the usual pattern, as with other infectious diseases caused by gram-negative bacteria. The first link of the immune response to the introduction of pathogens of pseudotuberculosis and yersiniosis is phagocytosis. Monocytes and neutrophilic leukocytes participate in protecting the body from bacterial aggression. Microbial bodies are actively captured by these cells. Inside some cells, bacteria decay and digestion or only partial digestion occurs; in others, microbial cells multiply. Subsequently, the multiplied bacteria lead to the death of the phagocyte and are released into the environment. At the first stages of the infectious process, incomplete phagocytosis is mainly observed. Macrophages turn into a “vehicle” for bacteria in the body. At this stage, whether there is a disease or not depends on the condition immune system human, virulence of incoming bacteria and other conditions.
Already at the first stages of contact between macrophages and bacteria, neutrophils are sensitized and damaged, which leads to a delay in the humoral response. From the 6-8th day of illness, globulins of three classes, general and immune, appear with a predominance of immunoglobulin M. At a later date (2-3 weeks of illness), antibody titers increase and double. During this period, antibodies can be detected by most diagnostic methods. Immunoglobulins M reach their maximum value by the end of the 2nd week. Then there is a switch to the production of class G immunoglobulins.
Thus, the formation of an immune response occurs by the 4-5th week, when humoral immunity reaches its maximum values. There is a peak in class G immunoglobulins. After an illness and full recovery immunoglobulins of class A disappear after 5 months, M - persist for 1-3 months and disappear after 6-8 months. Class G immunoglobulins last much longer.
In the case of the formation of a protracted course of the disease with damage to the joints (usually with yersiniosis), a persistent increase in the level of immunoglobulins of class A is observed. They, together with immunoglobulin G, can circulate for up to 2-3 years. After the disease, immune memory is formed in immunocompetent cells. Antibodies with complete recovery in yersiniosis are detected in decreasing titers up to 2-3 months; in pseudotuberculosis they cease to be detected even earlier. No repeated cases of yersiniosis and pseudotuberculosis were noted
In a healthy population, antibodies to Y. enterocolitica are observed in 2 to 50% of cases. The immune layer is higher in rural areas. Antibodies to the causative agent of pseudotuberculosis are not detected in healthy populations or are rarely found. In recent years, there has been a tendency towards an increase in the number of immune people in those places where their share was low. This indicates the evolution of the epidemic process and the intensity of its course.
Specific prevention of people with pseudotuberculosis has not been developed, although there is a need for its limited use. With yersiniosis, as with others intestinal infections, its feasibility has not yet been determined.
Depending on the nature of the development of the disease and the spread of bacteria in the human body, their release can occur with various substrates. In the first days of the disease, bacteria are found in the oropharynx, then in the blood and urine. During outbreaks of pseudotuberculosis, the majority of patients do not shed bacteria in their feces from the first days of illness. In patients with yersiniosis, when mostly from the first days there are symptoms of gastroentsrocolitis, bacteria are always present in the feces. In organ pathology, the release of bacteria from the body occurs periodically during exacerbations and relapses, and they can be in feces, urine, and less often in the blood.
Characteristics of the epidemic process. The emergence and increase in the incidence of pseudotuberculosis and yersiniosis are caused by a complex of socio-economic factors.
Urbanization, the inclusion of natural biotopes with natural biocenoses within cities, the settlement of cities with wild rodents that have become semi-synanthropic, led to the intensification epizootic process in the population of urban rodents. Intensive industrial development of livestock farming with predominantly stable housing of animals caused the formation of active foci and a significant increase in carriers of Yersinia, and, consequently, sources of pathogens. An increase in the population in cities, the concentration of various organized groups, the development of the food industry, public catering, and a decrease in sanitary and hygienic skills among personnel involved in obtaining, preparing and selling food products form factors for the transmission of infectious agents. The increase in the number of various storage facilities for food products and especially vegetables, where rotting of these products occurs, the active reproduction in this mass of various bacteria, including different types of Yersinia, determine the constant possibility of introducing contaminated products into the family and public catering units.
In this regard, in recent years there has been not only a statistical, but also a true increase in the incidence of pseudotuberculosis and yersiniosis and an increase in the number of cities and territories where these infections are recorded.
Yersiniosis and pseudotuberculosis are predominantly a disease of cities. For yersiniosis, constantly recorded sporadic incidence is more typical; group outbreaks are rare.
Pseudotuberculosis is characterized by a sporadic incidence, against the background of which outbreaks occur, mainly in organized groups. A long-term study of the incidence of pseudotuberculosis indicates the presence of periodicity; an increase in incidence after 2-3 years has been established.
Sporadic cases of pseudotuberculosis and yersiniosis occur in all seasons of the year. The rise in the incidence of pseudotuberculosis is caused by the appearance of outbreaks that occur mainly during the cold period, starting from February-March. In recent years, outbreaks in summer have begun to be recorded in all territories. health institutions, which shifted seasonality towards the summer months.
The increase in the incidence of yersiniosis is more pronounced in the autumn-winter period. The epidemic process of pseudotuberculosis and yersiniosis is characterized by sporadic and group incidence, as well as carriage.
Sporadic morbidity is formed from cases associated with various food products infected at their industrial production enterprises (milk, dairy products, meat products), fruits and vegetables from stores. The occurrence of these diseases is determined by the accidental exposure of individuals to an infected product.
Group diseases in families are determined by the introduction of an infected product into them, violation of sanitary standards for its preparation or storage. In this regard, these cases are also rare. When products contaminated with Yersinia are introduced into catering units for public catering or an organized group, an outbreak is formed, which is facilitated by the working conditions of the catering units, their sanitary condition, low level sanitary literacy and employee responsibility.
Outbreaks associated with public catering establishments, without a special tracking system, are usually not registered, since diseases are detected at the place of residence in different areas of the city or even in other cities and add to the sporadic incidence. In organized groups, under the influence of the same set of causal factors as in public catering establishments, outbreaks occur. They are characterized by the simultaneous appearance and coverage of a significant number of team members and service personnel. Nosocomial outbreaks (only yersiniosis) are infrequent and have their own characteristics: their size is limited by the need for close contact with the source and the implementation of the household route of transmission of the pathogen.
Carriage of pseudotuberculosis bacteria by practically healthy people has not been detected. After an illness, there is a long-term release of the pathogen due to the incomplete infectious process. After complete recovery, carriage disappears. With yersiniosis, carriage is uncommon, ranging from 1.5-2%. In some areas, an increase in the number of carriers is observed, which indicates the evolution of the epidemic process and the colonization of the human population by these bacteria.
Clinical and laboratory diagnostics. Incubation period from 1 to 6 days, more often up to 3 days. The disease begins without prodromal phenomena, acutely. With yersiniosis, symptoms of damage to the gastrointestinal tract, vomiting, abdominal pain, fever, and diarrhea predominate. The disease may end within 3-5 days or last up to 2 weeks. In some patients, following diarrhea syndrome, abdominal pain may increase, often in the ileocecal region, and symptoms of appendicitis or acute abdomen. In some cases, the liver enlarges, less often - the spleen, on the 3-7th day a rash appears, often polymorphic, intoxication and symptoms of damage to individual organs and systems increase (arthritis, hepatitis, less often - meningitis, eye damage) or a generalized infection, as determines the form of the disease. Young children often develop a generalized infection or sepsis early on. In more later periods, coinciding with the 2-3rd relapse, an allergic rash, erythema nodosum, arthritis, damage to the kidneys and eyes are noted.
With pseudotuberculosis, especially during outbreaks, the first manifestation is usually symptoms of intoxication - chills, headache, aches in the muscles, bones and lumbar region, sore throat when swallowing, dry cough, nasal congestion, increased body temperature. Hyperemia of the face, neck, upper chest, palms and soles, bright hyperemia of the mucous membrane of the soft palate, palatine arches, conjunctivitis, scleritis, and sometimes enanthema on the soft palate are detected. During the height of the disease (from the 2-5th day), a rash appears, often scarlet-like, which is localized on the chest, back, abdomen, limbs, less often the face, thickening in natural skin folds, often around the joints. In half of the patients, pain is detected in the right iliac region, sometimes in the hypochondrium (usually the right), the liver is enlarged, and less often the spleen is enlarged. On the first day of illness, the stool is normal; in a small part (10%) of patients, diarrhea appears on the 5-7th day. Patients are usually lethargic, adynamic, negative, and in rare cases meningeal syndrome is detected. Subsequently, the fever may be constant, wave-like or irregular. The duration of the febrile period is from 2-4 days to several weeks. Then the patients’ well-being improves, the temperature gradually normalizes, abdominal pain and arthralgia are relieved, the rash disappears, and from the 2nd week, large or fine-plate peeling of the skin of the soles and palms usually begins.
With yersiniosis and pseudotuberculosis, a relapse is possible in the 2-3rd week, which is characterized by the appearance of damage to individual organs or systems (hepatitis, arthritis, ileitis, mesenteric lymphadenitis). In the 4th week and later there may be a second relapse with pronounced allergic manifestations(erythema nodosum, allergic rashes). Depending on the predominance of certain symptoms, several forms of the clinical course of infection are distinguished
tions: septic, gastrointestinal, abdominal, catarrhal, secondary focal, subclinical. According to the severity of the disease, yersiniosis and pseudotuberculosis can be mild, moderate, acute or protracted. The disease (more often with yersiniosis) can result in the formation of long-term arthritis, polyadenitis and damage to the musculoskeletal system, or be an impetus for the development of immunopathological processes [Pokrovsky V.I., Yushchenko G.V., 1983].
To confirm the diagnosis of yersiniosis and pseudotuberculosis, bacteriological and serological methods are used. For bacteriological research, various material is taken depending on the timing and clinical manifestation diseases. In the first days of the disease, if there are changes in the pharynx, a smear is taken from the mucous membrane. All patients have stool and urine examined. According to indications, cerebrospinal fluid, sputum, bile, mesenteric lymph nodes or altered parts of the intestines and appendix, pus from abscesses, and blood are taken. For serological testing, blood is taken from a vein in all patients. The collected material is stored in the refrigerator before being sent to the laboratory. A buffered sodium chloride solution or an isotonic solution of sodium chloride (0.85%) of a slightly alkaline reaction is used as the accumulation medium.
Inoculated test tubes, including those with stool inoculation, are placed in the refrigerator and stored in it until positive inoculation, but no more than 15 days, with periodic inoculation on solid media (classical cold method). IN lately The “cold shock” technique has been successfully used to examine feces and other contaminated material. After a day of incubation in the refrigerator, the test tube with the material is placed in a refrigerator at a temperature of -12-18°C for 18-20 hours or at a temperature of -24-30°C for 2-3 hours. After growing in a thermostat, sowing is done on solid media. The “alkaline treatment” method is also recommended. From test tubes with feces kept in the refrigerator for a day, take 1 loop of material and mix with 0.5% KOH; after 2-5 minutes they are sown on a dense nutrient medium. Both techniques are aimed at suppressing foreign flora.
Endo agar or Serov's solid medium is used as a solid nutrient medium. The crops are grown in a thermostat at a temperature of 22-25° C.
Identification is carried out on standard Hiss media, according to which the isolated bacteria are divided into species. For strains with the properties of Y. enterocolitica, the biovar is determined.
To determine the serovar of an isolated culture of Y. enterocolitica, an agglutination reaction is performed on glass with serum against various serovars of this type of bacteria. Since the incidence of pseudotuberculosis is caused mainly by pathogens of the first serovar, seroidentification of the isolated culture may not be carried out.
To identify specific antibodies in the blood serum of patients, an agglutination reaction is performed with a typical or autostrain, or an indirect agglutination reaction (IDA) with commercial diagnostics of Y. pseudotuberculosis and Y. enterocolitica. Antibody titers taken into account during diagnosis are 1: 100, 1: 200. Determination of the dynamics of antibody titer in paired sera is considered mandatory. For the diagnosis of yersiniosis and pseudotuberculosis, other immunological reactions have been described, both to detect antibodies and antigens, but there is no industrial production of these drugs in our country yet.
The classical cold technique is also used to study various environmental objects, but its effectiveness is insignificant. To increase the inoculability of bacteria from vegetables and washings, the alkaline treatment method, as well as the method heatstroke- processing of the material after daily growing in the refrigerator at high temperature (41-42 ° C) for 18-24 hours. The method is also aimed at containing flora, in this case psychrophilic.
Prevention and measures to combat yersiniosis and pseudotuberculosis. The environmental features of these infections require the efforts of various departments - veterinary, agro-industrial and medical.
Measures aimed at the source of infectious agents are currently ineffective. It is impossible to influence the natural circulation of Yersinia in a natural focus, since it is practically impossible to destroy rodents and, therefore, improve the health of large areas. The fight against rodents inhabiting cities is difficult, but unlike natural ones in these foci, it must be carried out systematically and constantly, and primarily in facilities associated with the storage and preparation of food, in public catering establishments and organized groups.
In livestock farms where anthropogenic foci of yersiniosis are formed, it is necessary to monitor the incidence of disease in the livestock and carry out sanitary and veterinary measures to properly maintain animals and reduce the contamination of the environment. An important measure for these infections is to protect food products - potential transmission factors - from being contaminated with Yersinia. It should be carried out at all levels of receipt, storage and sale of food products (livestock and poultry farms, dairies, meat processing plants, vegetable warehouses, shops). This is, first of all, a set of sanitary and hygienic standards for storage, processing technology and timing of sale of the finished product and monitoring their strict implementation and, secondly, sanitary education of workers of these enterprises and the formation of high responsibility among them.
While these measures do not always ensure that food products are completely harmless and free from microbial contamination. The most unfavorable areas are vegetable stores and greenhouses, since the pathogens of pseudotuberculosis and yersiniosis are constantly present at these facilities. Consequently, all foods and especially vegetables can be contaminated with Yersinia. Due to this special meaning have measures aimed at preventing the entry of microbes into ready-made meals in catering units: compliance by catering unit staff with general sanitary rules and hygiene skills. The set of measures should include: mandatory allocation of premises for
primary processing of vegetables; strict separation of unpeeled vegetables from semi-finished products; using only good quality vegetables for salads, thoroughly cleaning, washing, preparing salads and eating them only on the same day; mandatory washing of fruits, herbs and vegetables, consumed whole or in pieces; strict adherence to the rules for storing food in refrigerators; tightening control measures over the operation of catering units in the event of infection of vegetables in the storage facility supplying them, as well as in the spring and summer.
Preventive measures are not always effective. In many ways, they depend on the thoroughness of their catering workers. When Yersinia is introduced into catering units and sanitary standards are violated, bacteria and their metabolic products may enter and accumulate in ready-made dishes and the formation of pathogen transmission factors that determine morbidity.
When diseases appear in a team, a set of anti-epidemic measures is carried out: prohibition of consumption without heat treatment of all types of vegetables and fruits available in food department warehouses; bacteriological examination of vegetable dishes, vegetables, other food products and ready-to-eat dishes, various utensils, equipment, utensils, etc.; mandatory disinfection and washing of all dishes, boiling cutlery, sanitary treatment of premises, warehouses, catering units, dining room and their disinfection.
Food service workers are examined bacteriologically to identify sick people, carriers, infected hands, and protective clothing. In a team where group diseases have occurred, all sick people are actively identified and hospitalized. In children's groups, observation (thermometry, examination) is organized for 7-10 days to identify new diseases and possible relapses. In family foci of pseudotuberculosis, special measures are not advisable; hygienic measures are usually sufficient. With yersiniosis, if there are small children in the house, a bacteriological examination of family members is necessary to identify possible carriers. In case of nosocomial spread of Yersinia, a set of measures should be carried out that are generally accepted for other infections.
Those who have recovered from the disease and are discharged from the hospital practically healthy can be allowed to join children's groups and work. Children are subject to mandatory medical supervision at their place of residence or in a child care facility to identify possible relapses.
Based on the epidemiological significance of individual parts of a complex ecological system, epidemiological surveillance for yersiniosis and pseudotuberculosis, first of all, it should include constant monitoring of the contamination of vegetables in storage facilities and livestock products in places of their processing.
The catering units of organized groups and public catering establishments should be under constant sanitary, hygienic and bacteriological control, especially in preschool institutions, as they are in the highest risk groups. These measures are intensified during the season of rising incidence, when the epidemiological situation becomes more complicated.
The most important are measures aimed at interrupting the transmission routes of infectious agents from enterprises that form a rural anthropogenic focus (livestock farms, poultry farms). This is important to prevent animal diseases, prevent contamination of products, stop the release of infected waste, manure and other waste into the environment, and prevent sporadic diseases of people involved in livestock farming. However, it is difficult to radically influence a rural active focus, since this is associated with significant restructuring and re-equipment technological processes and high material costs. Consequently, the only measure is compliance with sanitary and hygienic requirements.
It is important to constantly combat rodents in all urban and rural areas. The least anti-epidemic importance is the fight against rodents in natural foci, where it is practically impossible to influence the natural circulation of microorganisms.
The genus Yersinia was organized in 1946 and named (at the suggestion of van Loghem) in honor of Alexandre Yersin. Previously, bacteria of this genus were classified as genus Pasteurella. Now the genus Yersinia includes microorganisms of 11 species (Y. aldovae, Y. bercow, Y. enterocolitica, Y. fredenksenii, Y. intermedia, Y. kristensenii, Y. mollaretii, Y. pestis, Y. pseudotuberculosis, Y. rohdei and Y. ruckeri), type species - Y. pestis. Since 1954, bacteria of the genus Yersinia have been included in the Enterobacteriaceae family.
Morphology
Most often, Yersinia cells have an ovoid shape (coccobacilli); with increasing cultivation temperature (from 37 o C), the bacteria more often take the form of rods. They stain gram-negative, bipolar staining is possible (can serve as a differential sign when examining Y. pestis). Rods are prone to polymorphism, forming filamentous, flask-shaped or spherical (involutional) forms under suboptimal conditions (for example, on agar containing table salt). Depending on the species (some strains of Y. ruckeri and the species Y. pestis) and cultivation temperature, they can be mobile and immobile sporogenous rods (sometimes coccobacilli) measuring 1-3 x 0.5-0 8 µm. The bacteria are immobile at 37°C, but are mobile when grown at temperatures below 30°C (mobile species - peritrichous). Some strains of Y. ruckeri and all isolates of Y. pestis are immobile (but Brownian motion is very pronounced) and have a capsule, while other species have a capsular substance.
Y. pestis is characterized by a morphologically isolated nucleoid, most clearly visible in involutional giant cells, and a lack of motility.
Yersinia species form grayish-mucous (S-forms) or rough R-colonies, and transitional forms are also isolated. Virulent strains form R colonies. Microscopic examination of Y. pestis colonies reveals colonies of two types: young - microcolonies with uneven edges (“broken glass”), later they merge, forming delicate flat formations with scalloped edges (“lace handkerchiefs”), mature ones - large with a brown granular center uneven edges (“daisies”). Many, especially virulent, strains of Y. pestis are capable of producing a dark pigment and reducing dyes (Janus green, indigo, methylene blue) in dehydrogenation reactions. On slanted agar, after 48 hours at 28° C, a grayish-white coating forms, growing into the medium. In broth, after 48 hours they form a delicate film on the surface and a flaky sediment; when grown in an aerated broth, they give homogeneous growth; they also grow well on gelatin without causing its liquefaction.
On solid media, colonies of Y. enterocolitica are small, shiny, often convex with a bluish tint in transmitted light. When cultivated (48 hours at 37°C) on Endo medium, the colonies have a pinkish tint. The polymorphism of the colonies is weakly expressed. During aging, Y. enterocolitica often exhibits confluent growth. Bacteria exhibit pectinase activity; on pectin agar, colonies are surrounded by a liquefaction zone. When cultivated in liquid media, the microorganism causes them to become cloudy. It is generally accepted that virulent strains of Yersinia form predominantly R-colonies, but for Y. enterocolitica the formation of rough colonies is uncharacteristic.
Table 14. Non-pathogenic Yersinia isolated from humans
Table 15. Differential characteristics of bacteria of the genus Yersinia
|
Test or substrate |
Yersinia bercovieri |
Yersinia enterocolitica |
Yersinia frederiksenii |
Yersinia intermedia |
Yersinia kristensenii |
Yersinia mollaretii |
Yersinia pestis |
Yersinia pseudotuberculosis |
|
Indole formation | ||||||||
|
Voges-Proskauer reaction | ||||||||
|
Simmons Citrate | ||||||||
|
Urease activity | ||||||||
|
Ornithine decarboxylase | ||||||||
|
Melibiose fermentation | ||||||||
|
Raffinose fermentation | ||||||||
|
Sorbitol fermentation | ||||||||
|
Fermentation of sucrose | ||||||||
|
Fermentation of rhamnose | ||||||||
|
Fermentation of mucat |
* Possible positive reaction in freshly isolated strains.
This section uses the results of D.A. Pomerantsev’s dissertation work.
Table 16. Differential characteristics of bacteria of the genus Yersinia depending on the cultivation temperature (25-28°C / 37°C)
|
Test or substrate |
Y. enterocolitica |
Y. frederikseilii |
Y. pseudotuberculosis |
|||||
|
Voges-Proskauer reaction | ||||||||
|
Simmons Citrate | ||||||||
|
Mobility | ||||||||
|
Melibiose fermentation | ||||||||
|
Raffinose fermentation | ||||||||
|
Fermentation of rhamnose | ||||||||
|
Salicin fermentation | ||||||||
|
Fermentation of mucat | ||||||||
|
Hydrolysis of esculin | ||||||||
|
Urease activity |
Temperature limits for Yersinia growth vary from 0 to 39°C (for Y.pestis up to 45°C); optimum growth - 28-30°C; a temperature of 37°C is selective for the formation of a Y.pestis capsule. The pH limits for growth are within 5.8-8.0; optimum pH is 6.9-7.2. They grow well on simple nutrient media; the slow growth of bacteria (up to 3 days) can be accelerated by adding hemolyzed blood or sodium sulfate (Y. pseudotuberculosis practically does not grow on Ploskirev’s medium). The most favorable temperature for isolating Y. enterocolitica is 22-29°C. On motility media (eg, those containing indole and ornithine), Y. enterocolitica is immobile or inactive at 35°C and motile at 25°C.
Small coccobacteria with flagella, pili and a microcapsule. There is no dispute. They are characterized by bipolar coloring. Y. enterocolitica grows well on basic media over a wide temperature range. They can be classified as moderate psychrophiles.