Purpose: This project was designed to implement and validate environmental pathogen monitoring programs for Listeria monocytogenes and Salmonella in small dairy processing facilities.
Methods: Environmental sampling was performed at five cheese production facilities throughout New York State. Samples were analyzed by plating on selective media and polymerase chain reaction. The obtained pathogen isolates were further characterized by pulsed field gel electrophoresis (PFGE). Corrective action was suggested according to the results.
Results: A total of 1346 samples were collected. Of these, 34 (2.52%) tested positive for Listeria spp. and 35 (2.60%) were positive for L. monocytogenes. The prevalence of Listeria in a given plant varied from <1% (no Listeria detection) to 6.6%, whereas Salmonella was only detected in a single plant. While PFGE patterns suggest persistence of some L. monocytogenes strains in the processing environments, presence of multiple PFGE patterns in most plants suggested multiple contamination sources. Independent validation sampling (i.e., collection of samples from sites not routinely sampled) found similar L. monocytogenes prevalences as routine sampling, suggesting effective sampling plans.
Significance: This study provides a model for development and implementation of effective environmental pathogen monitoring programs. Importantly, we also present a procedure for validation of sampling plans through independent sampling from environmental sites not included in the routine sampling plans.