title: Effect of phage and host concentration on the inactivation of Escherichia coli O157:H7 on cooked and raw beef.
abstract: 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 (<100 CFU/cm(2)) or high (10(4) CFU/cm(2)) 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/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 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/cm(2)) for reductions to occur. A concentration of the order 8 log10 plaque forming units/cm(2) was needed to achieve a 4 log10 CFU/cm(2) reduction.
authors.affiliation: Food Programme, ESR Ltd, Ilam, Christchurch, New Zealand andrew.hudson@esr.cri.nz.
authors.forename: J A
authors.initials: JA
authors.lastname: Hudson
authors.affiliation: Food Programme, ESR Ltd, Ilam, Christchurch, New Zealand.
authors.forename: C
authors.initials: C
authors.lastname: Billington
authors.affiliation: Food Programme, ESR Ltd, Ilam, Christchurch, New Zealand.
authors.forename: T
authors.initials: T
authors.lastname: Wilson
authors.affiliation: Food Programme, ESR Ltd, Ilam, Christchurch, New Zealand.
authors.forename: S L W
authors.initials: SL
authors.lastname: On
mesh_terms: D000818:Animals; D001435:Bacteriophages; D002417:Cattle; D015169:Colony Count, Microbial; D003296:Cooking; D019453:Escherichia coli O157 / Q000254:growth & development*; D005511:Food Handling / Q000379:methods*; D005516:Food Microbiology; D005519:Food Preservation / Q000379:methods*; D061353:Food Storage; D006801:Humans; D050296:Microbial Viability; D000069466:Red Meat / Q000382:microbiology*; D013696:Temperature
keywords: Escherichia coli O157:H7; bacteriophage; biocontrol; food safety