Purpose: The purpose of this study was to determine if APC can be predictive of the probability of detecting L. monocytogenes on food and nonfood contact surfaces.
Methods: Twenty environmental swabs were collected monthly for three months from 20 retail produce departments across seven states (n=1,041). Sample sites included nine nonfood contact (NFCS) and 11 food contact surfaces (FCS). Prior to enrichment, an aliquot from each environmental sample was serially diluted and plated on Petrifilm™ aerobic count plates. Samples were subsequently tested for L. monocytogenes using the ROKA Atlas®LmG2 assay with confirmation of positives through secondary enrichment in Fraser broth followed by plating on RAIPID’L.mono plates.
Results: The highest APC were from floors, drains, squeegees, organic shelving, and standing water. A total of 7.7% (80 of 1,041) of samples were confirmed positive for L. monocytogenes; specifically, L. monocytogenes was found on 1.8% (10 of 571) of FCS and 14.9% (70 of 470) of NFCS. Using logistic regression, the odds of detecting L. monocytogenes increased 1.8-fold for every one-log increase in APC (P<0.0001). Surface type had an additional, separate effect, in that there was an 8.1-fold increase in the odds of detecting L. monocytogenes on NFCS versus FCS (P<0.0001).
Significance: This study supports that APC may be a cost-effective environmental monitoring tool to identify sanitation challenges that could potentially result in L. monocytogenes harborage. Using APC as a sanitation monitoring tool may have an additional benefit of indicating an opportunity for shelf life extension and food quality improvement.