Listeria monocytogenes from food and food industry environments with reduced susceptibility to benzalkonium chloride, sodium hypochlorite, and peracetic acid.

The growing number of Listeria monocytogenes strains displaying increased tolerance to sanitizers widely applied in the food industry is becoming a problem. The aims of this study were to evaluate the susceptibility of L. monocytogenes isolates from food and food industry environments to sanitizers (benzalkonium chloride, sodium hypochlorite, peracetic acid, and chlorhexidine) and heavy metals (cadmium chloride), as well as to investigate the presence of the main genes related to efflux pumps. All 82 isolates showed reduced susceptibility to benzalkonium chloride (MIC from 16 to 128 µg mL-1), sodium hypochlorite (MIC of ≥ 2048 µg mL-1), and peracetic acid (MIC from 512 to ≥ 2048 µg mL-1), while 22 isolates showed reduced susceptibility to cadmium chloride (MIC > 70 µg mL-1). Susceptibility to chlorhexidine was found (MIC from 2 to 16 µg mL-1). PCR-based analysis revealed that mdrl and lde genes were harbored by 14.6% (12/82) and 40.2% (33/82) of the isolates, respectively. This study demonstrates the presence of L. monocytogenes from food and food industry environments with reduced susceptibility to sanitizers commonly used in food processing environments, highlighting the importance of continuous monitoring of the tolerance profile of this microorganism to sanitizers, as well as the need for strict control of sanitation conditions in food industries.