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

The ability to preserve food in a state that is both appetising and nutritious is a basic requirement for health. Food poisoning represents a major source of illness and loss of productivity in many developed countries. Of particular concern in recent years are outbreaks of food poisoning associated with Escherichia coli O157:H7 or Listeria monocytogenes, many of which have been associated with the consumption of ground meat. Many of the chemicals presently licensed for use as food preservatives are increasingly being questioned 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 (LPS), for use in ground meat preparations is examined in this study. The degree 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°C and in a ground beef system at 0, 6 and 12°C. The degree of inhibition by LPS of natural populations of microorganisms present in ground beef obtained from eight retail outlets and incubated at room temperature was also examined. For each of the strains examined, sensitivity from most to least sensitive 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 temperature dependent and maximal at a temperature permissive but not optimal for growth of the test strain. The numbers of bacteria detected in ground beef obtained from retail outlets varied considerably between the eight samples. In all cases, numbers of bacteria increased markedly in the uninhibited control over the 4 h incubation time and, with the exception of one faecal coliform count, growth of the microbial populations was strongly inhibited by the presence of LPS. It was concluded that LPS could potentially be applied to a considerably wider range of food products than those to which it is presently restricted.