Cultural characteristics of Yersinia enterocolitica and Yersinia pseudotuberculosis on differential media.

A study was made of the cultural characteristics of 43 strains of Yersinia enterocolitica and 49 strains of Yersinia pseudotuberculosis on media commonly used for the isolation and differentiation of enteric bacteria. Best growth of the yersinia occurred on MacConkey agar, followed by growth on SS agar; none of the strains of either species developed colonies on brilliant green agar. The Y. pseudotuberculosis strains developed only one type of colony on MacConkey, SS, EMB, Hektoen, and XLD media whereas Y. enterocolitica exhibited more than one type of colony on all of the media except MacConkey and SS agar. The 'lactose-positive' colonies of Y. enterocolitica were especially distinctive on EMB. These were quite dark, with or without a metallic sheen, and closely resembled the colonies of lactose fermenting Escherichia coli on EMB agar. Strains of both Y. enterocolitica and Y. pseudotuberculosis grew better on the differential media at 35 degrees C than at 22 degrees C but the growth of Y. pseudotuberculosis was considerably slower than that of the other species.