Virulence and Antibiotic Resistance Genes in Listeria monocytogenes Strains Isolated From Ready-to-Eat Foods in Chile

Abstract

<i>Listeria monocytogenes</i> is causing listeriosis, a rare but severe foodborne infection. Listeriosis affects pregnant women, newborns, older adults, and immunocompromised individuals. Ready-to-eat (RTE) foods are the most common sources of transmission of the pathogen This study explored the virulence factors and antibiotic resistance in <i>L. monocytogenes</i> strains isolated from ready-to-eat (RTE) foods through <i>in vitro</i> and <i>in silico</i> testing by whole-genome sequencing (WGS). The overall positivity of <i>L. monocytogenes</i> in RTE food samples was 3.1% and 14 strains were isolated. <i>L. monocytogenes</i> ST8, ST2763, ST1, ST3, ST5, ST7, ST9, ST14, ST193, and ST451 sequence types were identified by average nucleotide identity, ribosomal multilocus sequence typing (rMLST), and core genome MLST. Seven isolates had serotype 1/2a, five 1/2b, one 4b, and one 1/2c. Three strains exhibited <i>in vitro</i> resistance to ampicillin and 100% of the strains carried the <i>fosX</i>, <i>lin</i>, <i>norB</i>, <i>mprF</i>, <i>tetA</i>, and <i>tetC</i> resistance genes. In addition, the <i>arsBC</i>, <i>bcrBC</i>, and <i>clpL</i> genes were detected, which conferred resistance to stress and disinfectants. All strains harbored <i>hlyA</i>, <i>prfA</i>, and <i>inlA</i> genes almost thirty-two the showed the <i>bsh, clpCEP, hly, hpt, iap/cwhA, inlA, inlB, ipeA, lspA, mpl, plcA, pclB, oat, pdgA</i>, and <i>prfA</i> genes. One isolate exhibited a type 11 premature stop codon (PMSC) in the <i>inlA</i> gene and another isolate a new mutation (deletion of A in position 819). The Inc18(rep25), Inc18(rep26), and N1011A plasmids and MGEs were found in nine isolates. Ten isolates showed CAS-Type II-B systems; in addition, Anti-CRISPR AcrIIA1 and AcrIIA3 phage-associated systems were detected in three genomes. These virulence and antibiotic resistance traits in the strains isolated in the RTE foods indicate a potential public health risk for consumers.