A PCR-based primary screening method for foods contaminated with enterohemorrhagic Escherichia coli (EHEC) O157 or O26 was developed. The method employs a multiplex PCR targeting EHEC O157 and O26 specific toxB sequences. The multiplex PCR assay was found to detect EHEC O157 and O26 but no other strains tested (except for several EHEC O121 strains). Experimental inoculation of a range of concentrations of EHEC O157 and O26 cells to overnight cultures of minced beef, beef liver or radish sprout in buffered peptone water (BPW), indicated that detection limit of the multiplex PCR assay was ca. 105 CFU/ml for EHEC O157 and O26. Subsequent quasi-field test, in which combinations of EHEC O157 or O26 strains were experimentally contaminated at an initial density of ca. 0.3 to 0.5 viable cells per gram of minced beef, beef liver or radish sprout, demonstrated that the multiplex PCR successfully detected EHEC O157 and O26 in the overnight cultures of the food samples in BPW. Based on the results, the multiplex PCR technique can be used as a primary screening tool for possible EHEC O157 and O26 contamination in food samples.
Two anamorphic fungi isolated from spoilt foods were identified as Arthrinium state of Apiospora montagnei and Arthrinium phaeospermum, respectively. The former fungus has been reported to cause the spoilage of packaging food products such as seasoned soy-sauce for Japanese noodles. The latter was involved in the spoilage of strawberry jam. Therefore, further study was conducted to be confirmed the response of these spoilages. The growth and gas formation of two isolates from the spoilt foods and additional fungi of Arthrinium state of Apiospora montagnei and A. phaeospermum were observed on inoculated YM broth in sealed pouches under extremely reduced oxygen tension. The results obtained indicate that the anaerobic growth of these fungi was observed and usually accompanied by formation of carbon dioxide and ethyl alcohol. The control of Arthrinium growth by elimination of oxygen is not feasible, because of their propagation in a GasPack anaerobic jar. On the other hand, only one strain of A. phaeospermum, which was isolated from the thermally processed strawberry jam, was responsible for thermal tolerance examination of spores.