Efficacy of using a sponge sampling method to recover low levels of Escherichia coli O157:H7, Salmonella typhimurium, and aerobic bacteria from beef carcass surface tissue

Recovery of aerobic bacterial populations, as well as low levels of Escherichia coil O157:H7 and Salmonella typhimurium from beef carcasses was determined by sponge (SP) and excision (EX) sampling during the course of three separate studies. For the first study, samples were taken from three points on the processing line: (1) pre-wash, (2) post-wash, and (3) after 24 h in the chill cooler. SP recovered fewer total aerobic bacteria from beef carcasses on a processing line than EX; however, the difference between EX and SP was similar at all sampled process points. Both sampling methods recovered higher levels of total aerobic bacteria from carcasses after a 24-h-chill period. Both methods also recovered low levels of E. coli and coliforms on beef carcasses. In the second study, both SP and EX recovered antibiotic-marked strains of E. coli O157:H7 and S. typhimurium from beef carcass tissue surface at an inoculation level of approximately 1 cfu 100 cm^-2. Recoveries from pre- or post-24-h-chilled tissue were similar for both SP and EX. SP appears to be an adequate sampling method for recovery of low levels of pathogens from surfaces of beef carcasses regardless of location within the process. However, a third study demonstrated that the freezing and storage of SP samples at -20°C significantly decreased recovery of S. typhimurium from beef tissue when present at low levels (≤ 10 cfu 100 cm^-2).