Yersinia Isolation HiVeg™ Agar

Principle And Interpretation

Yersinia is a gram-negative bacillus that is usually nitrate reductase-positive, fermentative, oxidase-negative and facultative with respect to oxygen requirement. Yersinia is usually urease-positive and motile at 25°C but not at 35°C. It is relatively sensitive to acidic conditions; therefore acid foods and fermented products should be analyzed promptly. A variety of enrichment methods have been described for recovery of Yersinia enterocolitica from foods. Highly selective enteric plating media, such as SS Agar (M108) have been used for isolation of Yersinia. Yersinia Isolation Agar has been developed for selective isolation of Yersinia species and preliminary differentiation of Y. enterocolitica from human and animal intestinal contents (1). The medium is recommended by the ISO Committee for identification of Yersinia species from foods (2). This medium is similar to composition as Yersinia Isolation Agar except the animal peptones and bile salts are replaced with vegetable peptones, extracts and synthetic detergent to avoid BSE/TSE risks associated with animal peptones.

HiVeg™ peptone, HiVeg™ extract No.1 and yeast extract provide nitrogenous and carbonaceous compounds, vitamin B complex, trace elements and other essential growth nutrients. Neutral red acts as the pH indicator. Lactose is the fermentable carbohydrate. Synthetic detergent inhibit Enterobacteriaceae but not Y.enterocolitica. Brilliant green and sodium citrate suppresses growth of accompanying gram-positive bacteria. Within 24 hours of incubation at 29-30°C, Y.enterocolitica and some species of Enterobacteriaceae exhibit scanty growth, however, after 48 hours, Y.enterocolitica colonies are well established and other Yersinia species start growing.

For isolation, streak the primary or secondary enrichment broths after incubation on one or more selective agar plates. After appropriate incubation period, examine the plates for colonies resembling Yersinia.