Method-Dependent Implications in Foodborne Pathogen Quantification: The Case of Survival on Meat as Comparatively Assessed by Colony Count and Viability PCR.

The aim of the present study was to address method-dependent implications during the quantification of viable cells on meat over time. Traditional colony counting on selective and non-selective culture media along with an optimized viability real-time PCR utilizing propidium monoazide-quantitative PCR (PMA-qPCR), spheroplast formation and an internal sample process control (ISPC), were comparatively evaluated for monitoring the survival of on fresh lamb meat during refrigeration storage under normal atmospheric conditions. On day zero of three independent experiments, lamb meat pieces were artificially inoculated with and then stored under refrigeration for up to 8 days. Three meat samples were tested on different days and the mean counts were determined per quantification method. An overall reduction of the viable on lamb meat was observed regardless of the applied quantification scheme, but the rate of reduction followed a method-dependent pattern, the highest being observed for colony counting on modified charcoal cefoperazone deoxycholate agar (mCCDA). Univariate ANOVA indicated that the mean counts of viable using PMA-qPCR were significantly higher compared to Columbia blood agar (CBA) plating (0.32 log cell equivalents, = 0.015) and significantly lower when mCCDA was compared to CBA plating (0.88 log CFU, < 0.001), indicating that selective culture on mCCDA largely underestimated the number of culturable cells during the course of meat storage. PMA-qPCR outperformed the classical colony counting in terms of quantifying both the culturable and viable but non-culturable (VBNC) cells, which were generated over time on meat and are potentially infectious and equally important from a public health perspective as their culturable counterparts.