Concurrent detection of Escherichia coli O157:H7 and Salmonella from a single enrichment in 24 h

The objective of this study was to determine ifa single assay protocol could result in the concurrent detection of Escherichia coli O157:H7 and Salmonella from a single sample grown in a single enrichment in 24 h. Twenty-Jive and 375 g of ground beef nonfat dry milk, and dry pet food samples were seeded with low (10 cfu/sample) and high (100 cfu/sample) levels off. coli O157:H7 and Salmonella cultures and incubated at 35 and 41C for 18 h for nonselective preenrichment. Incubated samples were analyzed by immunomagnetic separation (IMS) following a 6 h incubation for selective enrichment at 37C using M-broth and enzyme linked immumosorbent assay (ELISA). Depending on the food samples and the inoculation level, the minimum concurrent detection level off. coli O157:H7 and Salmonella was <I cfu/g in the samples at the competitor flora level of 10(5) cfu/g or less in ground beef samples, but in other cases of higher competitor loads and low target inoculations E. coli O157:H7 could not be detected in the presence of the Salmonella.