Relationships between the density of different indicator organisms on sheep and beef carcasses and in frozen beef and sheep meat

Abstract

To describe the relationship between the concentration of different indicator bacteria in red meat. Enumeration data for aerobic plate count (APC), Enterobacteriaceae, coliforms and Escherichia coli biotype I were analysed from an Australia-wide survey of beef carcasses, sheep carcasses, frozen beef and frozen sheep meat. In all commodities, there was only low-to-moderate rank correlation (0.16-0.47) between concentration of APC and concentration of each Gram-negative indicator. Rank correlations between counts of Gram-negative indicators were much higher (0.47-0.92) especially when nondetections were excluded from analysis (0.78-0.94). Receiver-operator characteristics analysis showed that detection of coliforms can predict the presence of E. coli biotype I with almost 100% sensitivity but fails to predict absence in 2.7-8.5% of samples not containing E. coli biotype I. Enumeration of coliforms is a useful adjunct to enumeration of E. coli biotype I or Enterobacteriaceae in red meat. The density of coliforms or Enterobacteriaceae can be used to predict the presence or absence of E. coli biotype I, although when the latter is at low prevalence errors in positive test prediction can be large. A quantitative basis is provided for comparing the concentration of different indicator bacteria measured in the production, regulation and trade of red meat.