Evaluation of an optical microbiological method for rapidly estimating populations of aerobic bacteria, coliforms, and Escherichia coli from ground pork

Abstract

The BioSys optical methods for estimating populations of aerobic bacteria, coliforms, and Escherichia coli from ground pork were evaluated. Ground pork samples were analyzed immediately, after temperature abuse at 25°C for various periods of time, or after temperature abuse and dilution by mixing with pork that was prepared by grinding whole muscles that had the outer portion excised using a sterile scalpel. Each ground pork sample was tested using standard methods such as aerobic plate counts (APC), violet red bile (VRB) agar plate counts (coliforms), and three-tube most probable numbers (MPN - E. coli). Each sample was tested using the BioSys for total viable counts (TVC) by placing 2 ml of ground pork homogenate (25 g into 225 ml of sterile 1% buffered peptone water) into 8 ml of nutrient medium containing brom-cresol purple in a test vial and monitoring at 35°C. Coliforms were enumerated by placing 5 ml of ground pork homogenate into 5 ml of coliform medium (CM) in a test vial and monitoring at 35°C. E. coli were enumerated by placing 5 ml of ground pork homogenate into 5 ml of double-strength CM with 2% dextrose in a test vial and monitoring at 42°C. The correlation coefficients for the regression lines comparing APC to BioSys TVC detection times (DT), VRB to BioSys coliform DT, and MPN to BioSys E. coli DT were -0.95, -0.94, and -0.93, and the line equations were log10 CFU/ml = 8.94 - 0.40(DT), log10 CFU/ml = 8.77 - 0.43(DT), and log10 CFU/ml = 8.96 - 0.81(DT), respectively. These methods may allow pork producers to monitor equipment surfaces and products in less than 16 h and obtain microbiological results prior to shipment.