Occurrence of Yersinia enterocolitica in Raw and Pasteurized Milk

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Abstract
Raw milk (100 samples) and pasteurized milk (100 samples) were assayed for presence of Yersinia enterocolitica, using four different enrichment and post-enrichment techniques. Isolation of Y. enterocolitica was made on MacConkey agar and Cefsulodin-Irgasan-Novobiocin (CIN) agar directly from incubated broths containing the milk, and after treatment of enrichment broths with a potassium hydroxide solution. Twelve samples of raw milk and one of pasteurized milk contained Y. enterocolitica. Nearly all isolates were found after KOH treatment. All isolates except that obtained from the pasteurized milk sample produced detectable levels of heat-stable enterotoxin. However, none of the 13 isolates agglutinated in WA-SAA, an antiserum specific for virulent Y. enterocolitica.