Viability of The Isolated Yersinia enterocolitica Strains from Damietta Cheese and Ice Cream at Different Refrigeration and Freezing Temperatures

Yersinia enterocolitica is considered one of the most prevalent pathogens transmitted through milk and milk products. Therefore, we aimed to detect the prevalence of these bacteria in cheese and ice cream and study the influence of refrigeration and freezing on its growth patterns. A total of 80 samples of cheese and ice cream were collected from Assiut city, Egypt (40 samples each). The collected samples were examined for the isolation of   Y. enterocolitica by the classical culture method and improved by the PCR technique. The incidence of Y. enterocolitica was 17.5 and 25.0 % in the examined cheese and ice cream samples by culture method, respectively, its prevalence in the tested cheese and ice cream samples basing on PCR were 7.5 and 15% since 42.8 and 60.0% of the isolated Y. enterocolotica were confirmed positive. Bio- typing and serotyping of the isolated strains revealed that 8 out of   the confirmed strains were pathogenic ; Y. enterocolitica serotype O: 3 was the most prevalent strain, and all of the pathogenic strains carried the virulent ail gene. Nearly similar growth patterns of Y. enterocolitica were recorded during storage of cheese at 4 ± 2°C and 30 ± 2ºC and, a significant difference was observed in the 3rd week, the organism found to be survived for 18 weeks with a mean value of 7.4 ± 0.5 and 6.9 ± 0.16 log cfu/ g for cheese stored at 4 ± 2°C and 30 ± 2°C respectively. In the case of ice cream, there was a significant difference between the behavior of Y. enterocolitica during freezing storage at -6 ± 2°Cand -18± 2ºC in the 2nd week, the mean value for the organism count on the 16th week was 5.3 ± 0.26 and      5.6 ± 0.39 log cfu/ g, respectively.