Production of emetic toxin (cereulide) by Bacillus cereus was quantified in various food sources. The amount of the emetic toxin in eight of the nine food samples implicated in vomitingtype food poisoning ranged from 0.02 to 1.28μg/g. The vomiting-type strain, B. cereus NC7401 was inoculated into various foods, and then incubated for 24 hr at 25°C. In farinaceous foods, the production of emetic-toxin was as high as that in the foods sample implicated in food poisoning. Growth and toxin production was inhibited in the foods cooked with vinegar, mayonnaise and catsup, due to decreased pH or acetic acid.
To evaluate the chromogenic substrate medium method for detecting coliform bacteria, we isolated 441 coliform bacterial colonies from 1, 165 food samples and inoculated them into various test media (lactose broth, colillert, fluorocult laurylsulfate X-GAL broth and X-GAL agar). With inoculation of 100-101 cfu, the results obtained from these four media coincided in 81.2% and the chromogenic substrate medium method was slightly superior to the traditional lactose fermentation method in sensitivity. Increasing the number of cells (>102 cfu) used for inoculation slightly changed the results, indicating that detecting coliform bacteria with these media requires 100-101 cfu for the initial inoculation. Next, we ried to identify the colonies associated with differences in results. As a result, 73 coloniesconsisting of 7 genera (15 species) were identified. Especially Enterobacter and Serratia showed a greater number. In conclusion, detection of coliform bacteria using chromogenic substrate media is equal to or higher than that by the traditional method (lactose broth) at least under the present experimental conditions. The chromogenic substrate medium method is useful because of the rapidity of detection, but particular attention should be given to detecting bacteria that belong to the genera Enterobacter and Serratia.
An assay to detect halophilic non-sporeforming anaerobic Gram nagative rods in seafish and shellfish on the market (Tapes japonica, Meretrix lusoria, Crassostrea gigas, Babyronia japonica, Iefteye flounder, Pandalus borealis, Metapenaeus joyneri, Sardinops melanosticta) using an enrichment culture with 2% NaC1 and simple plate agar with 2% NaC1 culture isolationprocedure was staudied. By the enrichment culture method, halophilic non-spore forming anaerobic Gram negative rode were detected in 50.8% of the seafish and shellfish. The detection rate of halophilic non-sporeforming anaerobic Gram negative rods from shellfish in the winter season was higher than that in summer (p<0.00 1 and p<0.029). Concentration of halophilic non-sporeforming anaerobic Gram negative rods in the alimentary canal of shellfish detected 4.3×103-18.8×103cfu/g in winter season. We compared 45 strains of halophilic anaerobic non-sporeforming Gram negative rods isolated from the sea shellfish with the Haloanaerobium praevalens DSM 2228 strain. All of these strains were obligate anaerobic Gram negative, non-sporeforming bacteria which proliferated optimally atapproximately 2-3% or ≥ 5% salt. DNA base composition was 26.9-33.2 M% guanosine plus cytosine. This strain of these isolates have negligible DNA homology with the H. praevalens DSM 2228 strain described previously. Acetic acid, butyric acid and propionic acid were the major glucose fermentation end products formed. Glucose, fructose, inositol, ribose, maltose and mannose were fermented. A number of additional biochemical and physiological tests were performed. On the basis of those characteristics, isolates were identified as the new Haloanaerobium species, H. butyricum JCM 9809.