Resumen de Effect of phage and host concentration on the inactivation of Escherichia coli O157:H7 on cooked and raw beef
John Andrew Hudson, C. Billington, T. Wilson, Stephen L. W. On
A previously described phage infecting Escherichia coli O157:H7 was added to raw and cooked beef pieces at concentrations ranging from 101–108 plaque forming units/cm2 to either low (<100 CFU/cm2) or high (104 CFU/cm2) concentrations of host bacterial cells. Incubation for up to 24 h 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 >4 log10 CFU/cm2 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 24 h 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 (>4–5 log10 plaque forming units/cm2) for reductions to occur. A concentration of the order 8 log10 plaque forming units/cm2 was needed to achieve a 4 log10 CFU/cm2 reduction.
