Abstract
Listeria monocytogenes is an important food-borne pathogen that can persist in food processing environments and thus contaminate food products. Benzalkonium chloride (BC) is a common disinfectant widely used in food industry. Selective pressure associated with exposure to BC may result in adaptation to this agent in L. monocytogenes. In this study, the effect of BC adaptation on susceptibility to antimicrobial agents and tolerance to environmental stresses, as well as the role of efflux pumps in BC adaptation were investigated in Listeria monocytogenes. Exposure of L. monocytogenes to progressively increasing concentrations of BC led to adaptation not only to BC but also to several other antimicrobial agents with different modes of action, including cefotaxime, cephalothin, ciprofloxacin, and ethidium bromide (EtBr), indicating that the disinfectant BC has the ability to select for antibiotic resistance. Reserpine, an efflux pump inhibitor, reduced minimum inhibitory concentrations (MICs) of cephalosporins, ciprofloxacin, and EtBr in BC adapted strains, indicating that efflux pumps are involved in cross-adaptation to these antimicrobial agents. Our results showed that expression levels of the efflux pump MdrL in the BC adapted strains increased significantly relative to the corresponding wild-type strains (P < 0.05), with the highest increase in one BC adapted strain named HL06BCA. Moreover, the knockout mutant HL06BCAΔmdrL showed impaired growth compared to that of HL06BCA when exposed to 2 μg/ml of BC. It suggests that efflux pump MdrL is associated with BC adaptation in L. monocytogenes. However, we did not find mdrL to be associated with cross-adaptation to cephalosporins, ciprofloxacin, and EtBr in HL06BCA. Additionally, increased sensitivity to acid, alkali, osmotic, ethanol, and oxidative stresses was observed in most strains after repeated exposure to BC. These results suggest rotation of different disinfectant is helpful to maintain high effectiveness of BC toward L. monocytogenes and ethanol and hydrogen peroxide are at least the appropriate candidates.
Highlights
Listeria monocytogenes is a facultative intracellular, non-spore forming Gram positive bacterium which causes the severe disease listeriosis which can lead to meningitis, septicemia and mononucleosis
Our study found that minimum inhibitory concentrations (MICs) of ciprofloxacin for most of the Benzalkonium chloride (BC) adapted strains decreased in the presence of reserpine, supporting that efflux pumps are involved in cross-adaptation to ciprofloxacin in BC adapted strains of L. monocytogenes
Our results suggest that Lde could not be involved in cross-resistance to ciprofloxacin in BC adapted strain of L. monocytogenes, this pump is found to be responsible for ciprofloxacin resistance in L. monocytogenes (Godreuil et al, 2003)
Summary
Listeria monocytogenes is a facultative intracellular, non-spore forming Gram positive bacterium which causes the severe disease listeriosis which can lead to meningitis, septicemia and mononucleosis. Adaptation to QACs develops when bacteria are frequently exposed to sub-inhibitory concentrations of QACs (Martínez-Suárez et al, 2016; Møretr et al, 2017). L. monocytogenes has been shown to adapt to QACs in many previous studies (Aase et al, 2000; To et al, 2002; Lundén et al, 2003; Romanova et al, 2006).
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Free) 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a call
