ORIGINAL ARTICLE Relationships between the density of different indicator organisms on sheep and beef carcasses and in frozen beef and sheep meat D. Jordan 1 , D. Phillips 2 , J. Sumner 3 , S. Morris 1 and I. Jenson 3 1 New South Wales Department of Primary Industries, Wollongbar, NSW, Australia 2 Symbio Alliance, Eight Mile Plains, Qld, Australia 3 Meat and Livestock Australia, North Sydney, NSW, Australia Introduction Indicator groups of bacteria are widely used as a measure of the hygienic characteristics of food and beverage. They have the advantage of being enumerated inexpensively and easily for quantifying the performance of a production process, when particular pathogens or spoilage organisms might be difficult to detect. When a general measure of process hygiene is required during meat production, the aerobic plate count (APC) is used to quantify the density of aerobic bacteria by unit area (e.g. carcass surfaces) or weight (e.g. meat trim). In addition to APC, there are three Gram-negative indicator groups (total Enterobacteriaceae, total coliforms and Escherichia coli biotype I) available for assessing the amount of contamination on meat arising from gut contents (including faeces), which includes both that originating directly from the alimentary track and that arising indirectly via the integument or processing environ- ment. In Australia, Canada, New Zealand and the USA, E. coli biotype I is the Gram-negative indicator that is most commonly used as a measure of faecal contamination in regulation and research (Biss and Hathaway 1995; Gill et al. 1996; Sofos et al. 1999; Phillips et al. 2001). In research, total coliforms are often concurrently enumerated with E. coli biotype I, because this requires little additional effort when dilutions are inoculated onto some modern Keywords beef, carcass, coliforms, Enterobacteriaceae, Escherichia coli, indicator, sheep meat. Correspondence David Jordan, New South Wales Department of Primary Industries, 1243 Bruxner Highway, Wollongbar, NSW 2477, Australia. E-mail: david.jordan@dpi.nsw.gov.au 2005/1514: received 21 December 2005, revised 9 April 2006 and accepted 24 April 2006 doi:10.1111/j.1365-2672.2006.03060.x Abstract Aim: To describe the relationship between the concentration of different indi- cator bacteria in red meat. Methods and Results: Enumeration data for aerobic plate count (APC), En- terobacteriaceae, 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 correla- tion (0Æ16–0Æ47) between concentration of APC and concentration of each Gram-negative indicator. Rank correlations between counts of Gram-negative indicators were much higher (0Æ47–0Æ92) especially when nondetections were excluded from analysis (0Æ78–0Æ94). 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 2Æ7–8Æ5% of sam- ples not containing E. coli biotype I. Conclusions: 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. Significance and Impact of the Study: A quantitative basis is provided for com- paring the concentration of different indicator bacteria measured in the production, regulation and trade of red meat. Journal of Applied Microbiology ISSN 1364-5072 ª 2006 The Department of Primary Industries for and on behalf of the state of New South Wales Journal compilation ª 2006 The Society for Applied Microbiology, Journal of Applied Microbiology 102 (2007) 57–64 57