Analysis of Genetic Determinants Encoding Resistance to Heavy Metals and Disinfectants in Listeria monocytogenes

<i>Listeria monocytogenes</i> is an important foodborne pathogen causing listeriosis. <i>L. monocytogenes</i>, existing in the natural environment, can also contaminate food products, which poses a serious threat to human health and life, especially for high-risk groups: pregnant women, newborn babies, and the elderly. Environmental adaptation of <i>L. monocytogenes</i> refers to the various strategies and mechanisms used by this bacterium to survive and thrive in diverse and often hostile environments that include, among others, toxic heavy metals and disinfectants. The aim of this study was to analyze WGS (whole-genome sequencing) data of 45 <i>L. monocytogenes</i> strains isolated from food to compare the prevalence and types of genetic determinants encoding resistance to toxic metals, such as arsenic and cadmium, as well as quaternary ammonium compounds, like benzalkonium chloride. In <i>L. monocytogenes</i> strains, resistance genes were detected for disinfectants, such as benzalkonium chloride (4.4%), as well as for toxic heavy metals, like cadmium (28.9%) and arsenic (24.4%). The <i>bcrABC</i> cassette was found together with the <i>cadA2C2</i> genes in two strains: 3855-D (IIc, ST9, CC9) and 4315 (IVb, ST6, CC6). The arsenic cassette, encoded by the genes <i>arsR1D2R2A2B1B2</i>, was co-selected with the <i>cadA4C4</i> genes. The arsenic cassette was prevalent in nine strains of clonal complex CC2 (82%), one strain of CC3 (9%), and one strain of CC11 (9%). In contrast, the benzalkonium chloride cassette was detected in one strain of CC6 and one strain of CC9. The results of the present study demonstrate the need for further research into the characteristics of <i>L. monocytogenes</i> isolated from other sources in order to understand their spread throughout the food chain.