Exposure to quaternary ammonium compounds selects resistance to ciprofloxacin in Listeria monocytogenes.

The increase of antibiotic resistance in foodborne bacteria is becoming of the main threat for public health. Increasing number of studies have shown that the exposure to disinfectant biocides as those daily used in the food industry may participate to increase antibiotic resistance in these bacteria. In this contribution, we assessed the antimicrobial susceptibility profiles toward 11 antibiotics and 4 biocides of a panel 206 Listeria monocytogenes strains from different origins. We also investigated the impact of repeated exposure to these biocides on the Lm antibiotic susceptibility. Results revealed that quaternary ammonium compounds (QACs) exposure of Lm strains often led to a decrease of susceptibility toward ciprofloxacin (CIP), a fluoroquinolone antibiotic, largely used in human and veterinary medicine and considered as a critically important antimicrobial. Furthermore, such susceptibility decrease remained stable in most Lm strains even after subcultures without biocide selection pressure suggesting an adaptation involving modifications at the genetic level. The extensive use of QACs in our environments may thus participate to the selection of critical antibiotic resistance in pathogen bacteria such as Lm and thus represent a public health issue