Purpose: This study verified the quantitative recovery, reproducibility, uncertainty and statistical difference (P<0.05) if any, between the 3M Petrifilm Rapid Aerobic Count (3M RAC) (AOAC OMA 2015.13, 35°C/24 h) and the 3M Petrifilm Aerobic Count (3M AC) (AOAC OMA 990.12, 35°C/48 h).
Methods: Two naturally contaminated samples (raw beef and raw ground beef) were purchased from a commercial establishment. Twenty sub-samples for each of the matrices were evaluated in comparison to the reference method per ISO 16140-3:2003. Study variables included different times, working shifts, days (10), lots (media, diluents) and analysts.
Results: The recovery, reproducibility and uncertainty obtained with the 3M RAC for the raw beef samples were comparable to the reference method (3.59 log CFU/g; 0.033 and 0.066 log CFU/g vs. 3.63 log CFU/g; 0.016 and 0.032 log CFU/g, respectively). Similarly the recovery, reproducibility and uncertainty obtained with the 3M RAC for the raw ground beef samples were comparable to the reference method (4.53 log CFU/g; 0.012 and 0.024 log CFU/g vs. 4.63 log CFU/g; 0.010 and 0.019 log CFU/g, respectively). Bland-Altman evaluation showed Bias values very close to zero (raw ground beef -0.12 and raw beef -0.05), demonstrating concordance between the two methods. For both samples, 3M RAC showed statistical equivalence P<0.05 (raw beef P=0.817 and raw ground beef P=0.394).
Significance: The 3M RAC method enabled reliable and rapid quantitative detection of aerobic bacteria in beef samples. The quantitative recovery with the new method was found to be statistically comparable to reference methodology and can provide actionable results to the food industry in as little as 24 h.