Use of a ground beef model to assess the effect of the lactoperoxidase system on the growth of Escherichia coli O157 : H7, Listeria monocytogenes andStaphylococcus aureus in red meat

The ability to preserve food in a state that is both appetising and nutriti ous is a basic requirement for health. Food poisoning represents a major so urce of illness and loss of productivity in many developed countries. Of pa rticular concern in recent years are outbreaks of food poisoning associated with Escherichia coli O157:H7 or Listeria monocytogenes, many of which hav e been associated with the consumption of ground meat. Many of the chemical s presently licensed for use as food preservatives are increasingly being q uestioned with regard to their effects on humans, creating pressure on food suppliers to consider the use of 'natural' alternatives to these chemical agents. The potential use of one such agent, the lactoperoxidase system (LP S), for use in ground meat preparations is examined in this study. The degr ee of inhibition of growth of E. coli O157:H7, L. monocytogenes L45 and S. aureus R37 by LPS was examined in a broth system at 37 degrees C and in a g round beef system at 0, 6 and 12 degrees C. The degree of inhibition by LPS of natural populations of microorganisms present in ground beef obtained f rom eight retail outlets and incubated at room temperature was also examine d. For each of the strains examined, sensitivity from most to least sensiti ve followed the order L. monocytogenes L45, S. aureus R37 and E. coli O157: H7. In each case the ability of LPS to inhibit growth was highly temperatur e dependent and maximal at a temperature permissive but not optimal for gro wth of the test strain. The numbers of bacteria detected in ground beef obt ained from retail outlets varied considerably between the eight samples. In all cases, numbers of bacteria increased markedly in the uninhibited contr ol over the 4 h incubation time and, with the exception of one faecal colif orm count, growth of the microbial populations was strongly inhibited by th e presence of LPS. It was concluded that LPS could potentially be applied t o a considerably wider range of food products than those to which it is pre sently restricted. (C) 2000 Elsevier Science B.V. All rights reserved.