Yersinia enterocolitica
(Enterobacteriaceae family — facultatively anaerobic, zoonotic pathogen)
General Characteristics
- Gram-negative rod (G –ve), non-spore forming.
- Motile at 22–25°C, but non-motile at 37°C.
- Non-capsulated, unlike Y. pestis.
- Lactose-negative, urease-positive.
- Biochemical tests:
- Catalase +, glucose +
- Oxidase, Indole, Citrate –
Distinguishing feature: Cold enrichment enhances its growth at 4°C.
Epidemiology
- Reservoir: Mainly pigs, also rodents and domestic animals.
- Transmission: Faecal-oral route → Consumption of contaminated pork, milk, ice cream, or water.
- Common in cold climates and winter seasons.
Pathogenesis
Y. enterocolitica primarily causes enteric (intestinal) diseases and rarely systemic illness.
Key steps:
- 1. Ingestion → colonisation of ileum/colon.
- 2. Attachment: via invasins and adhesins.
- 3. Invasion of M cells of Peyer’s patches.
- 4. Proliferation in mesenteric lymph nodes.
- 5. Induces inflammation → mimics appendicitis.
Diseases Caused
- Enterocolitis / Gastroenteritis
- Watery or bloody diarrhoea, fever, abdominal pain.
- More severe in children and infants.
- Mesenteric lymphadenitis
- Mimics appendicitis; can lead to misdiagnosis.
- Reactive arthritis (post-infection) in HLA-B27 positive individuals.
- Erythema nodosum (painful red nodules, esp. on legs) – delayed hypersensitivity.
Systemic infections (like sepsis) are rare but can occur in immunocompromised patients.