Distribution, adhesion, virulence and antibiotic resistance of persistent Listeria monocytogenes in a pig slaughterhouse in Brazil

Listeria monocytogenes is a relevant pathogen usually associated with meat and ready-to-eat products. This study aimed to assess the distribution, adhesion, virulence and antibiotic resistance of L. monocytogenes in a pork production chain. Environment, carcass and food samples (n = 894) were obtained from different steps of a pork production chain over a 6-month period (10 samplings), including from farms and the slaughterhouse (reception, slaughtering, processing, storage and end products). L. monocytogenes was detected in samples from the reception (lairage floor, 1/10), slaughtering (drains, 2/20) and cutting room stages (conveyor belts in the final packing stage - 11/20, knife - 1/40, and cutting boards - 1/20). Positive results for conveyor belts were recorded in seven consecutive samplings. L. monocytogenes isolates (n = 87) were characterized as belonging to serogroup IVb and presented positive PCR results for inlA, inlB, inlC, inlJ, hlyA, plcA, actA and iap. Isolates were selected according to the original samples (n = 31) and subjected to Pulsed Field Gel Electrophoresis (PFGE), demonstrating their high clonal identity (98.4-100%). According to PFGE results and their original samples, isolates were selected (n = 16) and subjected to phenotypic assay to assess their adhesion potential and tested for resistance against 15 antibiotics; all tested isolates presented weak adhesion potential and were resistant to ampicillin. The present study demonstrated the persistence of L. monocytogenes in the pork processing facility, indicating the potential risk for cross-contamination with a potential virulent and resistant clone.