Isolation of shiga toxin-producing Escherichia coli (STEC) from foods using EHEC agar

Enterohaemorrhagic Escherichia coli (EHEC) agar was evaluated for its abili ty to recover one isolate of each of three serotypes (O157:H7, O26 and O113 :H21) of shiga toxin-producing E. coli (STEC) from raw mince, pasteurized m ilk and salami after enrichment. The method detected around one colony-form ing unit (cfu) in 25 ml in milk, but was less sensitive with salami, requir ing 10-1000 cfu 25 g(-1) (depending on serotype) for detection. In raw minc ed beef any enterohaemolysin-producing colonies were outnumbered by other c olonies and only one of 12 enrichments yielded the inoculum serotype. Addit ional tests were conducted on 15 retail meat products. One 25-g sample of e ach product was processed as purchased, while another was inoculated with 1 57-185 cfu of a cocktail of E. coli O157, O113 and O26 cultures. Recovery w as easily achieved with cooked meat products and salami. Recovery from raw minced meat was again difficult, but sometimes possible. Testing more suspe ct colonies than were tested in this study would presumably increase the se nsitivity of the method.