A total of 394 samples of fresh seafoods and ready-to-eat seafoods were collected from supermarkets in Tokyo, Kanagawa and Chiba for the study of Listeria spp. and Listeria monocytogenes contamination. Listeria spp. and L. monocytogenes were isolated from 10.2% and 5.8% samples, respectively. Most of the L. monocytogenes positive samples were ready-to in smoked salmon (4.3cfu/g) and boiled octopus (1.5cfu/g). The predominant serotype of L. monocytogenes was 1/2a, followed by 3a and 4b.
We evaluated the ability of the 5'-nuclease (TaqMan) PCR assay by Commercial Detection Kit to detect Shigatoxin-producing Escherichia coli O157 in pure cultures, inoculated raw ground meat, shrimp and vegetable enrichment samples. The results were compared with the culture method, standard PCR assay and ELISA. The TaqMan PCR was able to identify the organism when 102 cfu/ml or more organisms were present in pure culture and in novobiocin-modified EC enrichment of several food samples. In comparison, the recovery efficiency on CTSMAC plate was from 101 to 106 cfu/ml, standard PCR assay sensitivity was 104 cfu/ml or more organisms, and ELISA test showed false positive in contaminated samples of Citrobacter freundii. Our findings indicate that TaqMan PCR assay is a useful automatic assay for identifying the existence of E. coli O157 in food samples with a high detection sensitivity and results in two days.
The performance of Rapid Media-DO (RM-DO, Morinaga Milk Industry Co., Ltd.), a culture medium for rapid testing of coliforms, was experimentally examined. RM-DO is a prepared culture medium poured and solidified in Petri dishes in advance of testing. After a test sample is inoculated on the medium, allowed to absorb into it, and incubated, colonies that form on the surface of the medium are counted. RM-DO is prepared by dissolving powdered ingredients as in desoxycholate agar medium but with a greater amount of water than usual, and adjusting the water content by drying it to the prescribed level. As a result, RM-DO is able to absorb much more test sample than a conventionally-prepared plate (0.1-0.2ml), and it absorbed 1ml of a test sample within 30 minutes. The growth of coliforms was rapid in RM-DO, because bacteria grew on its surface, and there was no effect of heat from the poured medium, so that the incubation period could be shortened to 12 hours compared with that by the desoxycholate pour plate method (20±2 hours). In addition, the confirmatory test for coliforms could be performed simply and rapidly by directly dripping X-GAL/dimethylformamide solution over the colonies on the surface of the medium. In a comparative study with other media using milk inoculated with coliforms as well as raw milk, both bacterial counts and detection rate in RM-DO were comparable or superior to those by the desoxycholate agar pour plate method.