Does Shiga Toxin-Producing Escherichia coli and Listeria monocytogenes Contribute Significantly to the Burden of Antimicrobial Resistance in Uruguay?

Abstract

Shiga toxin-producing <i>Escherichia coli</i> (STEC) and <i>Listeria monocytogenes</i> are worldwide recognized zoonotic pathogens. Recent reports have emerged about the circulation of antimicrobial-resistant STEC and <i>L. monocytogenes</i> isolates. To assess the frequency of antimicrobial resistance and related genes in these pathogens, we studied 45 STEC and 50 <i>L. monocytogenes</i> isolates locally recovered from different sources. Antimicrobial susceptibility testing was performed by disk-diffusion method, and the genomic sequences of three selected STEC and from all 50 <i>L. monocytogenes</i> isolates were analyzed for antibiotic resistance genes. Four STEC and three <i>L. monocytogenes</i> isolates were phenotypically resistant to at least one of the antibiotics tested. Resistance genes <i>aph</i>(3″)-Ib, <i>aph</i>(3')-Ia, <i>aph</i>(6)-Id, <i>bla</i> _<i>T</i> _EM-1B, <i>sul</i>2, <i>mef</i> (A), and <i>tet(</i>A) were found in a human STEC ampicillin-resistant isolate. All <i>L. monocytogenes</i> isolates harbored f<i>osX, lin, mdr</i>L, <i>lde fepA</i>, and <i>norB</i>. Overall resistance in <i>L. monocytogenes</i> and STEC was low or middle. However, the high load of resistance genes found, even in susceptible isolates, suggests that these pathogens could contribute to the burden of antimicrobial resistance.