The genus Yersinia contains of 3 human pathogenic species, Y. enterocolitica, Y. pseudotuberculosis and Y. pestis, among which, Y. enterocolitica finds a major importance in food-borne cases.
Epidemiology: Yersinia are gram-negative straight rods or small cocci (0.5-0.8µm) and non-motile at 37°C but motile at temperature below 30°C. They are facultative anaerobic and do not produce H2S. They can grow at temperatures as low as 0oC, and the increased use of refrigeration in food chain may play a role in the increase in prevalence of these organisms. Different serotypes of Y.enterocolitica are associated with human infections in different regions of the world. As with other foodborne illnesses, the infection is transmitted by faecal-oral route. Toxin produce.
Clinical features: Gastroenteritis or mesenteric adenitis are the important clinical features. Severe abdominal pain, diarrheoa, fever; blood in stool; polyarthritis, erythema nodosum, especially in children is seen.
Diagnosis: Y. enterocolitica being psychrophilic, the sample is inoculated into a non-selective medium such as 1/15 M PBS and incubated at 4 °C for 21 days. Alternatively, selective enrichment broth such as bile oxalate sorbose (BOS) broth, irgasan ticarcillin chlorate (ITC) broth, peptone-sorbitol-bile salt broth (PSB) may be used at incubation temperature from 22°C to 25°C for fewer days (2-5 days). Selective media used are cefsulodin irgasan novobiocin agar (CIN) on which red bulls eye colonies appear. Virulent Yersinia enterocolitica agar (VYE) showing red colony, Salmonella-Shigella deoxycholate calcium chloride agar (SSDC) and MacConkey agar showing small, round colorless colonies are also used for isolation of Y. enterocolitica. The plasmid (PYV) along with heat stable enterotoxin gene yst, the invasive associated ail and inv and virF gene are used for the detection of virulence Y. enterocolitica by