Isolation and survival of "Yersinia enterocolitica" in ice cream at different pH values, stored at -18ºC

The presence of "Yersinia enterocolitica" was investigated in 203 samples of industrial (123) and non-industrial ice cream (80). Two "Y. enterocolitica" strains were isolated from non-industrial ice cream, which suggests the possibility of post-manufacturing contamination. One strain was typed as B:1A, O:3,50,51; lis Xz, while the other one was biotyped as B:1A but not serologically typed. Survival of "Y. enterocolitica" was investigated by inoculating nine samples of industrially manufactured ice cream to contain 20 CFU/ml of "Y. enterocolitica" and stored at -18ºC for 480 days. The inoculated samples were classified into three different groups according to their pH (Group 1: pH 4-5; Group 2: pH 5-6 and Group 3: pH 6-7). Viability was determined by a contamination of direct plating and enrichment. In Group 1, "Y. enterocolitica" was not detected after 150 days of storage, while in Groups 2 and 3, this microorganism was isolated until day 480 of storage. These fidings suggest that the survival time of "Y. enterocolitica" in ice cream stored at -18ºC is significantly (p<=0.05) lower at pH values under 5.

Protective immunity induced by a Yersinia enterocolitica serovar 0: 8 cellular extract

The purpose of this study was to investigate the protective power of a cellular extract (CE) from Y. enterocolitica 0:8 grown in condition of expression of chromosomal antigens. Mice were immunized by s.c. route and challenged with: 0 LD50 (1 x 10(4) CFU/ml). Immunoblotting showed that CE-specific serum reacted with several CE antigens. Prominent bands, of molecular weights 60 and 35.5, were present in cytoplasmic and membrane fraction, respectively. The lipopolysaccharide (LPS) was detected in CE. These findings suggest that chromosomally-encoded antigens present in CE may induce protection against Y. enterocolitica infection. Both humoral and cellular immune response contribute to protection in mice.