A new differential plate medium, CAL (cellobiose-arginine-lysine) agar, was developed and evaluated for the isolation of Yersinia enterocolitica. For all but two isolates tested, distinctive colonies were formed on CAL agar within 40 h of incubation at 25 degrees C. These colonies were readily recognized and isolated from a mixed inoculum containing 10 other bacteria commonly found in water and fecal specimens. Y. enterocolitica was presumptively identified based on colonial morphology from 9 of 10 fecal cultures containing the organism when inoculated to CAL agar and incubated for 40 h at 25 degrees C. No false-positive identification were made. The medium has been shown to be as sensitive as MacConkey agar in supporting growth of Y. enterocolitica, and it can be used in broth from for enumeration of the organism from water and liquid specimens. The medium is easily made and does not need to be autoclaved.
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