Survival and Growth of Bacterial Pathogens on Raw Meat During Chilling

Bacillus cereus 41°F 41°F 8.3 hr (19) Campylobacter jejuni 86°F (19) Clostridium botulinum nonproteolytic 37.9°F (19) Clostridium botulinum proteolytic 50°F (19) Clostridium perfringens 53.6°F 53.6°F 11.5 hr (19) Escherichia coli SF 44.6°F 46.8°F 40 hr 6.9 hr (19, 26) E. coli O157:H7 35.6°F no growth (1) E. coli O157:H7, pH 5.7 53.6°F 16.2 hr 6.0 hr (27) E. coli O157:H7, pH 6.3 53.6°F 2.78 hr 3.9 hr (27) Listeria monocytogenes 32°F 39.2°F 22.8 hr (19) Listeria monocytogenes 39.2°F 9.3 hr (22) Salmonella typhimurium 41°F 50°F 45 hr 9.65 hr (19, 26) Staphylococcus aureus 44.6°F (19) Yersinia enterocolitica 30.2°F 41°F 16.53 hr (18, 19) Yersinia enterocolitica 50°F 12.73 hr (18) Introduction Intact tissues from healthy animals are sterile. However, when these animals are slaughtered, bacteria from the hide, the gut, or the processing environment may contaminate the surfaces of meat. This occurs despite of washing animals before slaughter, various treatments to clean carcasses during processing, and programs to keep the environment clean. Some of these organisms are spoilage bacteria while others are pathogenic to humans. Many bacteria are unable to grow at low temperatures but can survive storage in the cold. Generally, numbers of viable bacterial cells decrease with time during refrigerated storage (1, 3, 4, 21). Other bacteria, including Listeria, Yersinia, some strains of Clostridium botulinum and Bacillus cereus, and some spoilage organisms, are psychrotrophic and can grow at refrigeration temperatures (Table 1). However, growth during chilled storage is usually slow (18). Several research papers have described protocols and experimental results for determining the hygienic adequacy of cooling processes by considering published data on growth rates of pathogens and the temperature history of the meat (2, 9–16). Temperature is not the only factor limiting growth of bacteria. Experiments have shown that bacteria grow more slowly on meat at a more acidic (lower) pH (25). Washing carcasses with organic acids, trisodium phosphate, or alkaline solutions significantly decreases pathogen levels (5, 6). Some pathogenic bacteria are not very good competitors and grow much more slowly in the presence of other bacteria that may be present on meat. Air cooling process may cause drying at the surface of the meat and this inhibits bacterial growth. For these reasons, one cannot simply extrapolate growth data from bacteria grown in the lab to commercial cooling processes. Survival and Growth of Bacterial Pathogens on Raw Meat During Chilling