Growth and survival of E-coli O157 : H7 during the manufacture and ripening of a smear-ripened cheese produced from raw milk

Aims: The behaviour of Escherichia coli O157:H7 was studied during the manu facture and ripening of a smear-ripened cheese produced from raw milk. Methods and Results: Cheese was manufactured on a laboratory scale using mi lk (20 1) inoculated with E. coli O157:H7, and enumeration was carried out using CT-SMAC. From an initial level of 1.52 +/- 0.03 log cfu ml(-1) in the milk (34 +/- 2 cfu ml(-1)), the numbers increased to 3.4 +/- 0.05 log cfu g(-1) in the cheese at day 1. During ripening, the numbers decreased to <1 cfu g(-1) and <10 cfu g(-1) in the rind and core, respectively, after 21 da ys, although viable cells were detected by enrichment after 90 days. The pr esence of E. coli O157:H7 in the cheese was confirmed by latex agglutinatio n and by multiplex PCR. Conclusions: The results indicate that the manufacturing procedure encourag ed substantial growth off. coli O157:H7 to levels that permitted survival d uring ripening and extended storage. Significance and Impact of the Study: The presence of low numbers of E. col i O157:H7 in milk, destined for raw milk cheese manufacture, could constitu te a threat to the consumer.