Comparison of the Traditional Three-Tube Most Probable Number Method with the Petrifilm, SimPlate, BioSys Optical, and Bactometer Conductance Methods for Enumerating Escherichia coli from Chicken Carcasses and Ground Beef

Abstract

A study was conducted to compare commonly used methods, such as Petrifilm and SimPlate, and the rapid microbiological methods BioSys optical and Bactometer conductance to the standard most probable number (MPN) procedure for enumerating Escherichia coli from poultry carcasses and ground beef. Broiler carcasses and ground beef were evaluated in each of three replicate trials. Five groups of carcasses or ground beef were sampled and analyzed using Petrifilm, SimPlate, BioSys optical, and Bactometer conductance measurements after temperature abuse at 37°C for 0 (Petrifilm and SimPlate only), 2, 4, 6, or 8 h. The correlation coefficients for the regression lines comparing the standard E. coli MPN procedure to Petrifilm and SimPlate for chicken and ground beef, respectively, were as follows: 0.95, 0.94, 0.93, and 0.91. The correlation coefficients for the regression lines comparing the standard E. coli MPN procedure to BioSys optical and Bactometer conductance measurements for chicken and ground beef, respectively, were −0.91, −0.90, −0.93, and −0.96. Although Petrifilm and SimPlate performed well, E. coli could not be enumerated from 16.7 and 10% of samples, respectively, using these methods. The BioSys optical and Bactometer conductance methods performed very well when compared with Petrifilm and SimPlate. Using rapid methods (BioSys optical and Bactometer conductance), results were obtained in 1 to 11 h rather than the 48 h required to conduct Petrifilm or SimPlate or the 5 days required to conduct the MPN procedure. These methods may allow processors to test products and obtain results before shipping, avoiding the cost and loss of reputation associated with a recall or foodborne illness outbreak.