Isolation methods for Yersinia enterocolitica from meat: Selectivity of CIN [cefsulodin-irgasan-novobiocin] medium and effect of alkali treatment

The effectiveness of CIN medium as a selective differential medium for Yersinia enterocolitica and that of alkali treatment for recovery of Yersinia species after PBS cold enrichment were evaluated using a total of 94 strains; 45 strains of Yersinia species and 49 strains of other species. All 45 strains of Yersinia grew on CIN medium forming colonies with a deep red center and translucent in the periphery. Of the 49 non-Yersinia strains, 21 strains of Citrobacter, Morganella, Serratia or Pseudomonas grew on the medium, but the colony forms of these strains were clearly different from that of Yersinia. Yersinia showed comparatively high resistance to alkali and the viable cell count was reduced to only 1/10-1/100 after treatment with 0.4% potassium hydroxide solution for 15-30 seconds. On the other hand, many of the non-Yersinia strains did not survive treatment with 0.4% or less potassium hydroxide solution for a short time. Under our experimental conditions with Yersinia and non-Yersinia strains, treatment with 0.4% potassium hydroxide solution for 30 seconds is appropriate for the recovery of Yersinia. It is suggested that combined use of alkali treatment after PBS cold enrichment and isolation with CIN medium is the most effective isolation procedure for Y. enterocolitica from meat.