Submitted to: Applied and Environmental Microbiology
Publication Type: Peer reviewed journal
Publication Acceptance Date: 7/16/2012
Publication Date: 10/23/2012
Citation: Ratani, S.S., Siletzky, R.M., Dutta, V., Yildirim, S., Osborne, J.A., Lin, W., Hitchins, A.D., Ward, T.J., Kathariou, S. 2012. Heavy metal and disinfectant resistance of Listeria monocytogenes from foods and food processing plants. Applied and Environmental Microbiology. 78(19):6938-6945. Interpretive Summary: Listeria monocytogenes is a food-borne bacterium that places a serious burden on human health and the agricultural economy. However, not al L. monocytogenes strains are equally likely to persist in food environments. In this study, we characterized a panel of L. monocytogenes from foods and processing plant environments in terms of their resistance to heavy metals and to the ammonium disinfectant benzalkonium chloride. We identified significant differences in the frequency of heavy metal and disinfectant-resistant strains between environmentally adapted subtypes in comparison to those that are more commonly responsible for human illness. We also identified a substantial number of isolates with putatively novel mechanisms of resistance to heavy metals. These data provide new information about the mechanisms used by L. monocytogenes to persist in different environments and will be of direct interest to epidemiologists, public health and food inspection agencies, and scientists involved in food safety research.
Technical Abstract: The persistence of Listeria monocytogenes in food processing plants and other ecosystems can be attributed to its ability to adapt to numerous stresses. Resistance to arsenic, cadmium and the quaternary ammonium compound benzalkonium chloride (BC) are examples of such adaptations. In this study, we investigated 138 isolates from foods and food processing plants for resistance to arsenic, cadmium and BC and determined the prevalence of three cadmium resistance determinants (cadA1, cadA2 and cadA3) among cadmium-resistant strains. Arsenic resistance was encountered primarily in serotype 4b and was an attribute of most isolates of the serotype 4b epidemic clonal group ECIa. Prevalence of the known cadmium resistance determinants was serotype-associated: cadA1 was more common in serotype 1/2a and 1/2b than 4b while cadA2 was more common in serotype 4b. A subset (15/77, 19%) of the cadmium-resistant isolates lacked the known cadmium resistance determinants. Most of these isolates were of serotype 4b and were also resistant to arsenic, suggesting novel determinants that may confer resistance to cadmium and arsenic in these serotype 4b strains. The distribution of heavy metal resistance attributes and determinants observed in this study may reflect components of the ecological history of different serotypes and clonal groups of L. monocytogenes, including exposures of the microorganisms to cadmium or arsenic.