Comparison of a Dry Medium Culture Plate (Petrifilm SM Plates) Method to the Aerobic Plate Count Method for Enumeration of Mesophilic Aerobic Colony-Forming Units in Fresh Ground Beef

Abstract

MATERIALS AND METHODS ABSTRACT Mesophilic aerobic microbial populations in fresh ground beef were enumerated with a new system, Petrifilm™ SM Plates (PSM), and with the conventional aerobic plate count (APC) method using standard methods agar (SMA). Total colony-forming units were determined in 119 fresh ground beef sam-ples (29 extra-lean, 30 lean and 60 regular) purchased at nine different retail markets over a period of 6 wk. Linear regression analysis of PSM vs. APC counts gave a slope of 0.963, an intercept of -0.027, and a correlation coefficient of 0.951. Mean log ] 0 counts on PSM were 5.86 compared to 6.11 on SMA (P<0.01) or a mean log ] 0 difference of -0.25. These analyses indicate that the Petrifilm SM method would be a pos-sible alternative for the aerobic plate count method. The microbiological quality of ground beef is of con-cern to the foodservice industry and often is evaluated by colony count procedures. Considerable effort has been directed to determine the microbial levels of ground beef (2,4). A new dry medium system, Petrifilm™ SM Plates (PSM), has been developed as an alternative to the aerobic plate count (APC) method for the enumeration of total aerobic mesophilic bacteria. A report by Ginn et al. (1) indicated a satisfactory performance with raw milk samples using the new PSM method. The objectives of this study were to evaluate the comparability of the PSM method to the APC method employing standard methods agar (SMA) and to compare the enumeration data generated by the two methods.