Use of a bacteriophage to inactivate Escherichia coli O157:H7 on beef

A number of outbreaks of Escherichia coli O157:H7 infections involving beef have been reported. Options for controlling bacterial pathogens in raw foods are limited, but one is to use bacteriophages (phages). We describe the isolation and characterisation of phage FAHEc1, which infects E. coli O157, and its ability to kill its host in vitro and on beef. The phage belonged to the family Myoviridae and lysed 28 of 30 E. coli O157 (:H7, :HNM and :H not specified) isolates, only one other non-O157 E. coli serotype (O162:H7), and none of the other 13 bacterial species tested. The phage did not contain stx1, stx2, eae or ehxA virulence genes as assessed by PCR. An approximate 4 log10 inactivation of E. coli O157:H7 occurred at 5 °C in the presence of phage FAHEc1 at >107 PFU/ml in broth in vitro. On thinly sliced beef pieces incubated at 37 °C, a > 2.7 log10 reduction occurred with 3.2 × 107 PFU/4 cm2 meat piece. At lower phage concentrations (103-104 PFU/4 cm2 piece) phage replication occurred on beef at 37 °C. When the phage was applied to beef pieces under conditions simulating hot boning and conventional carcass cooling, inactivation of E. coli O157:H7 of approximately 2 log10 was measured under optimal conditions with phages applied at 3.2 × 107 PFU/4 cm2 meat piece.