Abstract
To decide how to store food samples for a bacterial test of Shigella sonnei, its survival rate was assessed in saline and various foods such as canned young corn, raw oyster, raw ark shell, raw shrimp and raw cuttlefish at 4°C and -20°C for 13 days . The survival rate of S.sonnei in saline and in food uncontaminated with other bacteria at 4°C storage was better than that at -20°C. On the other hand, the survival of the organisms at -20°C storage was better than that at 4°C in the case of contaminated foods.
We investigated the influence on S. sonnei by Escherichia coli using two new methods for S. sonnei. Briefly, they are methods of direct anaerobic culture and of anaerobic culture after aerobic enrichment culture established by the Japanese Ministry of Health and Welfare in 2002. In addition, we performed recovery experiments for S. sonnei using various foods such as canned young corn, raw oyster, raw ark shell and raw shrimp. The sensitivity of both methods was influenced by E. coli and/or other bacteria. Furthermore, the PCR method showed better sensitivity than the traditional incubation method in both culture methods. Although we were able to detect S. sonnei up to ≤10-1 CFU/g in the cases of uncontaminated food, the sensitivity was changed by the kind of foods in the cases of contaminated foods using both methods. These results suggest that either of the two methods and two storage conditions could be chosen depending on the kind of foods.
