Abstract
Reduced susceptibility of Listeria monocytogenes to benzalkonium chloride (BC), a quaternary ammonium compound widely used in food processing and hospital environments, is a growing public health and food safety concern. The minimal inhibitory concentration of BC on 392 L. monocytogenes strains from Switzerland (CH) and Finland (FIN) was determined. Within this strain collection, benzalkonium chloride resistance was observed in 12.3% (24/195) of Swiss and 10.6% (21/197) of Finnish strains. In both countries, the highest prevalence of BC-resistant strains (CH: 29.4%; FIN: 38.9%) was detected among serotype 1/2c strains. Based on PCR analysis, genes coding for the qacH efflux pump system were detected for most of the BC-resistant strains (CH: 62.5%; FIN: 52.4%). Some Swiss BC-resistant strains harbored genes coding for the bcrABC (16.7%) efflux pump system, while one Finnish BC-resistant strain harbored the emrE gene previously only described among BC-resistant L. monocytogenes strains from Canada. Interestingly, a subset of BC-resistant strains (CH: 5/24, 20.8%; FIN: 9/21, 42.8%) lacked genes for efflux pumps currently known to confer BC resistance in L. monocytogenes. BC resistance analysis in presence of reserpine showed that the resistance was completely or partially efflux pump dependent in 10 out of the 14 strains lacking the known BC resistance genes. Sequence types 155 and ST403 were over-representated among these strains suggesting that these strains might share similar but yet unknown mechanisms of BC resistance.
Highlights
IntroductionThe causative agent of listeriosis in humans and animals, represents a major foodborne pathogen with serious impacts on public health and the food industry (de Valk et al, 2005; Popovic et al, 2014; Crim et al, 2015)
Listeria monocytogenes, the causative agent of listeriosis in humans and animals, represents a major foodborne pathogen with serious impacts on public health and the food industry
L. monocytogenes strains with low susceptibility to benzalkonium chloride (BC) have been regularly isolated from foods and food processing environments. (Mereghetti et al, 2000; Romanova et al, 2002; Mullapudi et al, 2008; Fox et al, 2011)., Benzalkonium chloride resistant (BCr) strains have been isolated from human listeriosis infections (Elhanafi et al, 2010), and there is evidence of cross-protection against other antimicrobials including gentamicin and ciprofloxacin (Rakic-Martinez et al, 2011)
Summary
The causative agent of listeriosis in humans and animals, represents a major foodborne pathogen with serious impacts on public health and the food industry (de Valk et al, 2005; Popovic et al, 2014; Crim et al, 2015). Quaternary ammonium compounds (QACs) such as benzalkonium chloride (BC), are widely used for cleaning and disinfection of food processing environments (McDonnell and Russell, 1999; Mereghetti et al, 2000). (Mereghetti et al, 2000; Romanova et al, 2002; Mullapudi et al, 2008; Fox et al, 2011)., Benzalkonium chloride resistant (BCr) strains have been isolated from human listeriosis infections (Elhanafi et al, 2010), and there is evidence of cross-protection against other antimicrobials including gentamicin and ciprofloxacin (Rakic-Martinez et al, 2011). The presence of BCr strains in food and food processing environments is concerning
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