Sources and extent of microbiological contamination of beef carcasses in seven United States slaughtering plants

This study determined microbiological loads of beef carcasses at different stages during the slaughtering to chilling process in seven (four steer/hei fer and three cow/bull) plants. Potential sources of contamination (feces, air, lymph nodes) were also tested. Each facility was visited twice, once i n November through January (wet season) and again in May through June (dry season). Carcasses were sampled by aseptic excision of surface tissue (100 cm(2)) from the brisket, flank, and rump (30 samples each) after hide remov al (pre-evisceration), after final carcass washing, and after 24-h carcass chilling. The samples were analyzed individually by standard procedures for aerobic plate counts (APC), total coliform counts (TCC), Escherichia coli biotype I counts (ECC), and presence of Salmonella. Incidence of Salmonella was higher on dry feces of older compared to younger animals, fresh feces of younger compared to older animals, and on cow/bull carcasses compared to steer/heifer carcasses. Most factors and their interactions had significan t (P less than or equal to 0.05) effects on the bacterial counts obtained. Depending on plant and season, APC, TCC, and ECC were less than or equal to 10(4), less than or equal to 10(2), and less than or equal to 10(1) CFU/cm (2) in 46.7 to 93.3, 50.0 to 100.0, and 74.7 to 100.0% of the samples, resp ectively. TCC exceeded 10(3) CFU/cm(2) in 2.5% (wet season) and 1.5% (dry s eason) of the samples. ECC exceeded 10(2) CFU/cm(2) in 8.7%, 0.3%, and 1.5% of the pre-evisceration, final carcass-washing, and 24-h carcass-chilling samples, respectively, during the wet season; the corresponding numbers dur ing the dry season were 3.5%, 2.2%, and 3.0%, respectively. These data shou ld serve as a baseline for future comparisons in measuring the microbiologi cal status of beef carcasses, as the new inspection requirements are implem ented.