Comparison of Conventional Plating Methods and Petrifilm for the Recovery of Microorganisms in a Ground Beef Processing Facility

Abstract

The objective of this study was to compare recovery of microorganisms for various beef samples and beef contact surfaces using conventional pour plating techniques and Petrifilm methods. Comparisons for aerobic plate count (APC), coliform count (CC), and Escherichia coli count (ECC) were done for 104 fresh or frozen retail cuts and 56 food surface or food contact surfaces. Samples were taken at a midwestern retail ground beef processing plant during a 12-month project. APC comparisons were made for pour plating using Trypticase soy agar versus Aerobic Plate Count Petrifilm. CC and ECC were compared for pour plating using violet red bile + MUG agar versus E. coli Petrifilm. Overall, paired t tests revealed a significantly higher recovery for APC from fresh and frozen beef samples using the pour plating technique (P ≤ 0.05). No significant differences (P > 0.05) were observed for CC from fresh and frozen meat samples. Recovery of E. coli from many beef samples was better using Petrifilm. Significantly higher ECCs were observed from fresh and frozen meat samples using Petrifilm compared to the pour plating technique (P ≤ 0.05). For food surfaces and food contact surfaces, a comparison between pour plating and Petrifilm was done for aerobic plate count. No significant differences (P > 0.05) in recovery could be found between methods. A comparison between neutralizing buffer and letheen broth for recovery of surface microorganisms was done for both the APC pour plating method and APC Petrifilm. In both cases, recovery when using letheen broth was significantly (P ≤ 0.05) higher than neutralizing buffer. Because it is convenient and gave comparative results, Petrifilm offers a good alternative for environmental microbial testing and red meat product testing.