Effect of phage and host concentration on the inactivation of Escherichia coli O157:H7 on cooked and raw beef

A previously described phage infecting Escherichia coli O157:H7 was added to raw and cooked beef pieces at concentrations ranging from 10(1)-10(8) plaque forming units/cm(2) to either low (<100CFU/cm(2)) or high (10(4)CFU/cm(2)) concentrations of host bacterial cells. Incubation for up to 24h was performed at 5? and 24? to simulate refrigerated and room temperature storage/temperature abuse. Surviving bacteria were enumerated during the incubation period, with phages being counted at the first and last sampling times. Significant reductions of E. coli O157:H7 of the order of >4log(10)CFU/cm(2) at both temperatures could be achieved compared to phage-free controls. There was a trend for greater inactivation to occur with increasing phage concentration. While re-growth of surviving cells occurred in nearly all samples incubated for 24h at 24?, these conditions are not typical of those experienced by perishable foods. It was concluded that phages can be used to reduce the concentration of a bacterial pathogen on meat, but the concentration of phages needs to be high (>4-5log(10) plaque forming units/cm(2)) for reductions to occur. A concentration of the order 8log(10) plaque forming units/cm(2) was needed to achieve a 4log(10)CFU/cm(2) reduction.