Pathogen characteristics
Yersiniosis is caused by bacteria of the family Enterobacteriaceae, genus Yersinia: Yersinia pseudotuberculosis (causes pseudotuberculosis) and Yersinia enterocolitica (causes intestinal yersiniosis).
These are Gram-negative, non-spore-forming, non-encapsulated bacteria. An important feature is their antigenic structure: thermostable O-antigens (determine the serogroup), surface K-antigens, and thermolabile H-antigens (formed only at temperatures below +28°C).
Ecologically, yersiniae are psychrophiles (optimal growth at +22–28°C, but they multiply even at 0°C) and oligotrophs (can grow on poor media, consuming nitrogen and carbon from air). This allows them not only to survive but also to actively accumulate in the environment, for example, in refrigerators and vegetable storage facilities.
Pathogenicity factors
The synthesis of aggression factors depends on environmental conditions and is controlled by chromosomes and plasmids.
- In the external environment (up to +28°C): bacteria are motile (have flagella), their cell wall contains full endotoxin, and they are highly virulent. Invasins are synthesized to facilitate penetration through the intestinal epithelium.
- In the warm-blooded organism: yersiniae lose motility and become low-virulent, but as they move toward the intestine, plasmid genes (such as pYV) are activated.
- Surface Yop proteins: act at later stages, ensuring adhesion, invasion (via intestinal M cells), and suppression of the immune response (anti-phagocytic activity, inhibition of chemotaxis, induction of macrophage apoptosis).
Additionally, Y. pseudotuberculosis and certain biovars of Y. enterocolitica synthesize yersiniabactin, an iron-scavenging system from the host's blood that promotes bacterial multiplication, especially in patients with iron overload.
Epidemiology
Yersiniosis infections are saprozoonoses.
- Reservoirs: primary is soil and water bodies, where the pathogen multiplies; secondary is animals, most often rodents, which excrete bacteria in urine and feces.
- Routes of infection: the leading mechanism is fecal-oral. Humans are infected alimentarily via contaminated vegetables, fruits (main factor), dairy, and meat products (especially pork).
- Conditions of infection: an obligatory factor is the accumulation of bacteria at low temperatures (in a refrigerator or basement), which sharply increases their virulence and infectious dose.
- Risk groups: primarily affects children aged 3–14 years. The incidence is usually sporadic or clustered, peaking in the winter-spring months (the period of maximum consumption of stored vegetables).
Briefly: answers to topical questions
What clinical forms are distinguished in the classification of intestinal yersiniosis?
The classification of yersiniosis includes four main clinical forms. The following forms and their variants are distinguished:
- Gastrointestinal form — gastroenteritis, enterocolitis, gastroenterocolitis.
- Abdominal form — acute appendicitis, mesenteric lymphadenitis, terminal ileitis.
- Generalized form — hepatitis, pyelonephritis, meningitis, pneumonia, mixed (including scarlatiniform), septic.
- Secondary focal form — arthritis, erythema nodosum, oculourethrosynovial syndrome, myocarditis, thyroiditis, enterocolitis.
What specific diseases and complications result from the antigenic mimicry of Yersinia with the HLA-B27 antigen?
Antigenic mimicry between Yersinia and host tissue antigens, particularly HLA-B27, leads to decreased recognition of microbial antigens by the immune system, persistence of the pathogen, and the development of immunopathological reactions.
The specific list of diseases and complications arising directly from this mimicry with HLA-B27 is not explicitly stated in the provided sources.
What laboratory diagnostic methods are used to confirm yersiniosis?
Bacteriological, serological, and early diagnostic methods are used for the laboratory confirmation of yersiniosis.
- Bacteriological method — stool culture on selective nutrient media with obligatory preliminary cold enrichment.
- Serological method — detection of rising titers of specific antibodies in paired sera using indirect hemagglutination inhibition assays (IHA) and agglutination assays (AA), as well as antigen detection in blood serum via ELISA.
- Early diagnostic methods — detection of pathogen antigens in saliva and coprofiltrates using the co-agglutination test.
Which groups of antibacterial drugs are the drugs of choice for etiotropic therapy of yersiniosis?
Fluoroquinolones and semisynthetic tetracyclines are the drugs of choice for empirical antibiotic therapy of yersiniosis.
- Fluoroquinolones (e.g., ciprofloxacin) — prescribed for moderately severe cases.
- Semisynthetic tetracyclines — used until laboratory test results are available.
- Chloramphenicol — is the drug of choice for yersiniosis meningitis.
In yersiniosis sepsis, combination antibiotic therapy is indicated based on the pathogen's susceptibility according to the antibiogram.
To remember the properties of Yersinia: "Cold vegetables." Yersinia love the cold (psychrophiles) and are frequently transmitted via vegetables stored in cellars.
Class and exam questions
Why is yersiniosis often called the "disease of refrigerators"?
Because the pathogens are psychrophiles: they are capable not only of surviving but also of actively multiplying at low temperatures (0–4°C), accumulating on foods during storage in a refrigerator or vegetable storehouse.
How do environmental conditions affect the motility of Yersinia?
At ambient temperatures (up to +28°C), Yersinia are motile due to flagella. When entering a warm-blooded organism (above +37°C), they lose their flagella and become immotile.
What is antigenic mimicry in yersiniosis?
Yersinia share common antigens with host tissues (e.g., HLA-B27). This reduces their recognition by the immune system, promotes prolonged persistence, and leads to the development of immunopathological reactions.
What else to study on this topic
- Clinical forms of intestinal yersiniosis
- Symptoms of pseudotuberculosis
- Laboratory diagnostic methods ("cold enrichment")
- Treatment and prevention of yersiniosis
- Mechanisms of action of Yop proteins
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