Purpose: (i) To investigate the biofilm formation potential of strains of different origin and lineages under various environmental conditions and (ii) to correlate biofilm formation with resistant mechanisms of the pathogen to biocides.
Methods: Twenty-three strains from various food processing equipment and food products were evaluated for attachment potential on polystyrene microplates in Tryptic Soy Broth (TSB) or TSB/10, after 72h at 20 or 37°C. Minimum inhibitory (MIC) and bactericidal (MBC) concentrations were evaluated for peroxyacetic acid (PAA) and quaternary ammonium compounds (QACs). Hydrophobicity of cell surface, and comparative resistance of biofilms, formed on stainless still and polystyrene, to 2000 ppm PAA and 500 ppm QACs for 5 min were evaluated. Experiments were performed in three technical and three biological replicates.
Results: Results revealed that biofilm formation was correlated with strain origin, environmental conditions and cell surface hydrophobicity. Equipment isolates were able to attach in higher populations to polystyrene in contrast to food isolates, and high electron donating nature contributed to higher attachment; no significant lineage effect was observed (P > 0.05). Strongly adherent strains were markedly influenced by growth conditions unlike weakly or moderately adherent strains, while exhibited the lowest MIC and MBC to PAA. Food isolates demonstrated higher resistance to biocides compared to equipment isolates. QACs and PAA effectiveness against biofilm cells were observed to increase on polystyrene and stainless steel, respectively, and both biocides were significantly more effective against biofilms formed on stainless still than those attached to polystyrene surface (P < 0.05).
Significance: Clarification of multivariate interactions between acquired and endogenous characteristics of L. monocytogenes may lead to design more accurate preventing systems to safety directions.