Purpose: Examine prevalence of genes encoding tolerance to disinfectants and their role under practical food industry conditions.
Methods: Isolates of Listeria monocytogenes (n=101) from Norwegian meat- and salmon processing plants were tested for the presence of qacH and bcrABC. The growth inhibitory effects of BC in suspension and bactericidal activity in biofilm (50 ppm) and suspension (10 ppm) were tested. The presence of BC was analysed in water remaining on surfaces in the food industry after sanitation.
Results: 23 and 8 of the isolates contained qacH and bcrABC, respectively. Isolates with qacH and bcrABC genes could multiply in higher concentrations of BC compared to isolates lacking these genes, however, they did not show increased tolerance to the biocidal effect of BC. Residues of BC were detected in all eight analysed samples of water residues collected from surfaces after sanitation. Two collected water samples with high concentration (>100 ppm) of BC had a bactericidal effect against L. monocytogenes, while a water sample with about 10 ppm BC had had different growth inhibition effects against L. monocytogenes with or without the qacH/bcrABC genes.
Significance: Low level tolerance to BC resulting from the presence of genes bcrABC and qacH may be advantageous for growth of L. monocytogenes in niches with residual disinfectant after practical cleaning and disinfection.