|Abstract||This National Standard Method (NSM) describes the identification of Yersinia enterocolitica and|
Yersinia pseudotuberculosis isolated from faeces. The organisms may also be isolated from other specimens such as blood, lymph nodes and abscesses.
The genus Yersinia belongs to the family Enterobacteriaceae and contains 11 species.
Yersinia species are Gram-negative rods. 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.
Principles of identification:
Isolates from primary faecal culture are identified by colonial appearance on selective media and
biochemical tests. If confirmation of identification is required, isolates should be sent to the Reference Laboratory. All identification tests should ideally be performed from non-selective agar.