Yersinia spp.
- Y. enterocolitica and Y. pseudotuberculosis are pleomorphic gram-negative bacilli in the family Enterobacteriaceae.
- They are non-lactose-fermenting, urease-positive organisms that grow at a wide range of temperature; they are motile at 25° C but not at 37° C.
- Y. enterocolitica colonies give a “bulls-eye” appearance on CIN (cefsulodin, Irgasan, novobiocin) medium. Y. pseudotuberculosis colonies on CIN medium are smaller with a deep-red centre with a sharp border surrounded by a translucent zone. Yersinia species are facultative anaerobes, oxidase-negative and ferment glucose with little or no gas production. They are non-motile at 37°C, but, with the exception of Y. pestis, are motile at 22 - 29°C. Phenotypic characteristics are often temperature dependent and more are expressed by cultures at 22– 29°C rather than 35 - 37°C.
- Both grow on BHI, MacConkey, and SS agars at room temperature and at 37° C, and in buffered saline at 4° C. Colonies are difficult to detect after incubation for 24 hours but are readily apparent at 48 hours.
- They can be distinguished from other enteric pathogens and from Y. pestis by biochemical profiles; however, rapid tests may be a cause of misidentification if not properly coded.
- More than 60 serotypes and six biotypes of Y. enterocolitica have been described. Most strains from patients belong to serotypes O:3, O:5.27, O:8, and O:9 and to biotypes 2, 3, and 4. There is a separate system for serotyping Y. pseudotuberculosis, also based on somatic antigens. Six serotypes (I through VI) and four subtypes of Y. pseudotuberculosis have been identified, with O-group I accounting for approximately 80% of human cases.
