ORIGINAL ARTICLE Characterization of an extremely heat-resistant Escherichia coli obtained from a beef processing facility E.A. Dlusskaya, L.M. McMullen and M.G. Ga ¨ nzle Department of Agricultural, Food and Nutritional Science, University of Alberta, Edmonton, AB, Canada Introduction Pathogen intervention treatments are widely used in beef processing to reduce the cell counts of pathogens on beef carcasses. Heat treatments are the most widely used inter- ventions in beef processing and common methods of application include hot water rinses, pasteurization with saturated steam, and steam vacuuming (Morgan et al. 1996; Nutsch et al. 1997; Castillo et al. 1998; Gill and Bryant 2000; Minihan et al. 2003; Sheridan 2004; Coran- tin et al. 2005; Rajic et al. 2007). Carcass washes with 2–4% lactic acid are also used for beef carcass decontami- nation in North America. The combined use of steam pasteurization and lactic acid washes reduces bacte- rial counts on the surface of beef carcasses by 90–99% (Smulders and Greer 1998). Despite the current pathogen intervention techniques used in beef processing, enterohaemorrhagic Escherichia coli (EHEC) remain a major concern to the meat industry and represent a potential public health risk. EHEC are etiological agents of haemorrhagic colitis, haemolytic ure- mic syndrome, and thrombotic thrombocytic purpura (Riley et al. 1983; Doyle and Schoeni 1984; Karmali 1989). The US Centre for Disease Control and Prevention estimates that 73 000 cases of illness annually are caused by Shiga toxin–producing E. coli in the US, resulting in 2000 hospitalizations and 60 deaths (Frenzen et al., 2005). The intestines of ruminant animals, including beef and dairy cattle, are the primary source of EHEC contamina- tion of food or water (Montenegro et al. 1990). Contami- nation of muscle tissues with EHEC during the beef slaughter process occurs primarily in the dehiding and evisceration steps (Barkocy-Gallagher et al. 2001;. Aslam et al. 2004). The presence of generic E. coli on beef is considered to be an indicator for pathogenic strains in the species Keywords acid resistance, beef processing, Escherichia coli, heat resistance, pathogen interventions. Correspondence Lynn M. McMullen, Department of Agricultural, Food and Nutritional Science, University of Alberta, 4-10 Ag ⁄ For Centre, Edmonton, AB, T6G 2P5 Canada. E-mail: lynn.mcmullen@ualberta.ca 2010 ⁄ 1405: received 12 August 2010, revised 20 December 2010 and accepted 4 January 2011 doi:10.1111/j.1365-2672.2011.04943.x Abstract Aims: This study aimed to determine the survival of Escherichia coli strains during steam and lactic acid decontamination interventions currently used by the beef-processing industry, and to determine their heat resistance. Methods and Results: Strains were grouped into cocktails of five strains each differing in their RAPD patterns for subsequent identification. Steam and lactic acid treatments on meat reduced cell counts of E. coli strain cocktails by 90– 99%. The 20 slaughter plant isolates exhibited only minor variation in their resistance to steam and lactic acid treatments but were more resistant than reference strains (three strains) or isolates from live cattle (seven strains). D 60 values of strains from live cattle, and reference strains ranged from 0Æ1 to 0Æ5 min, in keeping with literature data. However, D 60 values of current slaugh- ter plant isolates ranged between 15 for E. coli DM18.3 and 71 min AW 1.7. Cell counts of E. coli AW 1.7 were reduced by <5 log 10 CFU g )1 in ground beef patties cooked to an internal temperature of 71°C. Conclusions: Strains of E. coli that survive cooking of ground beef to the rec- ommended internal temperature of 71°C can be isolated from beef-processing facilities. Significance and Impact of the Study: Pathogen interventions in current com- mercial beef slaughter may select for extremely heat-resistant strains of E. coli. Journal of Applied Microbiology ISSN 1364-5072 840 Journal of Applied Microbiology 110, 840–849 ª 2011 The Society for Applied Microbiology ª 2011 The Authors