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.

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 samples (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 counts on PSM were 5.86 compared to 6.11 on SMA (P<0.01) or a mean log difference of -0.25. These analyses indicate that the Petrifilm SM method would be a possible alternative for the aerobic plate count method.