Biofilm-forming ability and biocide susceptibility of Listeria monocytogenes strains isolated from the ready-to-eat meat-based food products food chain

•Strong and moderate L. monocytogenes biofilms were associated to high LD90 values.•Benzalkonium chloride and sodium hypochlorite were active in most of the strains.•Nisin was not active against biofilms within the tested concentration range.•Three strains were resistant to all the tested biocides.

To assess the biofilm-forming ability of Listeria monocytogenes and its susceptibility to food-grade biocides, food (n = 120) and food contact equipment samples (n = 60) collected from the ready-to-eat meat-based food chain were analyzed. A total of 113 L. monocytogenes isolates were obtained and genetically characterized. Nineteen strains were tested for biofilm-forming ability and susceptibility to benzalkonium chloride, sodium hypochlorite and nisin. Most strains were moderate to strong biofilm-formers (crystal violet optical density ranging from 0.13 ± 0.03 to 0.20 ± 0.04). When treated with benzalkonium chloride and sodium hypochlorite, most biofilms were reduced, but the same did not happen with nisin. Three strains revealed a resistant profile to all biocides with high estimated LD90 values (≥1.79 mg/ml for benzalkonium chloride and sodium hypochloride and >1000 IU/ml for nisin). Biofilm-forming ability and LD90 values highlight the need to consider other sanitizers and novel strategies for mitigation and control of L. monocytogenes biofilms.