Manual squeezing as an alternative to mechanical stomaching in preparing beef carcass sponge samples for microbiological analysis.

The U.S. Department of Agriculture (USDA) requires beef abattoir operators to periodically analyze beef carcass sponge samples for levels of Escherichia coli. Additional beef carcass sponge sampling is commonly used by processors to evaluate the efficacy of beef abattoir antimicrobial intervention systems. The USDA sample preparation procedure requires that beef carcass sponge samples be mechanically stomached for 2 min before the sample fluid is squeezed out for analysis. When a large number of sponge samples must be analyzed, the stomaching step can limit throughput. In this study, we compared the USDA sample preparation procedure with repeatedly squeezing the sponge during a 10-s interval to expel the sample fluid. Separate sponge samples were obtained from each half of 100 chilled postintervention beef carcasses from a large-volume abattoir during a 4-month period. The USDA and squeezing treatments were randomly assigned to the halves of each carcass. All sponge samples were analyzed for E. coli, coliforms, Enterobacteriaceae, and aerobic mesophilic bacteria using Petrifilm methods. The sample preparation method had no significant effect (signed rank value > 0.05) on the results of any analytical test, although aerobic mesophilic bacteria counts tended to be higher after the USDA method than after manual squeezing alone. These results suggest that manual squeezing may be a simple and rapid alternative sample preparation method when gram-negative bacteria such as E. coli, coliforms, or Enterobacteriaceae are being enumerated from beef carcass sponge samples used to monitor operational abattoir hygiene.