Coselection of Cadmium and Benzalkonium Chloride Resistance in Conjugative Transfers from Nonpathogenic Listeria spp. to Other Listeriae

Abstract

ABSTRACTResistance to the quaternary ammonium disinfectant benzalkonium chloride (BC) may be an important contributor to the ability ofListeriaspp. to persist in the processing plant environment. Although a plasmid-borne disinfectant resistance cassette (bcrABC) has been identified inListeria monocytogenes, horizontal transfer of these genes has not been characterized. NonpathogenicListeriaspp. such asL. innocuaandL. welshimeriare more common thanL. monocytogenesin food processing environments and may contribute to the dissemination of disinfectant resistance genes in listeriae, includingL. monocytogenes. In this study, we investigated conjugative transfer of resistance to BC and to cadmium from nonpathogenicListeriaspp. to other nonpathogenic listeriae, as well as toL. monocytogenes. BC-resistantL. welshimeriandL. innocuaharboringbcrABC, along with the cadmium resistance determinantcadA2, were able to transfer resistance to other nonpathogenic listeriae as well as toL. monocytogenesof diverse serotypes, including strains from the 2011 cantaloupe outbreak. Transfer among nonpathogenicListeriaspp. was noticeably higher at 25°C than at 37°C, whereas acquisition of resistance byL. monocytogeneswas equally efficient at 25 and 37°C. When the nonpathogenic donors were resistant to both BC and cadmium, acquisition of cadmium resistance was an effective surrogate for transfer of resistance to BC, suggesting coselection between these resistance attributes. The results suggest that nonpathogenicListeriaspp. may behave as reservoirs for disinfectant and heavy metal resistance genes for other listeriae, including the pathogenic speciesL. monocytogenes.