AUTHOR=Frye Jonathan G., Jackson Charlene R.

TITLE=Genetic mechanisms of antimicrobial resistance identified in Salmonella enterica, Escherichia coli, and Enteroccocus spp. isolated from U.S. food animals

JOURNAL=Frontiers in Microbiology

VOLUME=4

YEAR=2013

URL=https://www.frontiersin.org/journals/microbiology/articles/10.3389/fmicb.2013.00135

DOI=10.3389/fmicb.2013.00135

ISSN=1664-302X

ABSTRACT=<p>The prevalence of antimicrobial resistance (AR) in bacteria isolated from U.S. food animals has increased over the last several decades as have concerns of AR foodborne zoonotic human infections. Resistance mechanisms identified in U.S. animal isolates of <italic>Salmonella enterica</italic> included resistance to aminoglycosides (e.g., alleles of <italic>aacC</italic>, <italic>aadA</italic>, <italic>aadB</italic>, <italic>ant</italic>, <italic>aphA</italic>, and <italic>StrAB</italic>), β-lactams (e.g., <italic>bla</italic><sub>CMY−2, TEM−1, PSE−1</sub>), chloramphenicol (e.g., <italic>floR, cmlA, cat1, cat2</italic>), folate pathway inhibitors (e.g., alleles of <italic>sul</italic> and <italic>dfr</italic>), and tetracycline [e.g., alleles of <italic>tet</italic>(A), (B), (C), (D), (G), and <italic>tetR</italic>]. In the U.S., multi-drug resistance (MDR) mechanisms in <italic>Salmonella</italic> animal isolates were associated with integrons, or mobile genetic elements (MGEs) such as IncA/C plasmids which can be transferred among bacteria. It is thought that AR <italic>Salmonella</italic> originates in food animals and is transmitted through food to humans. However, some AR <italic>Salmonella</italic> isolated from humans in the U.S. have different AR elements than those isolated from food animals, suggesting a different etiology for some AR human infections. The AR mechanisms identified in isolates from outside the U.S. are also predominantly different. For example the extended spectrum β-lactamases (ESBLs) are found in human and animal isolates globally; however, in the U.S., ESBLs thus far have only been found in human and not food animal isolates. Commensal bacteria in animals including <italic>Escherichia coli</italic> and <italic>Enterococcus</italic> spp. may be reservoirs for AR mechanisms. Many of the AR genes and MGEs found in <italic>E. coli</italic> isolated from U.S. animals are similar to those found in <italic>Salmonella</italic>. <italic>Enterococcus</italic> spp. isolated from animals frequently carry MGEs with AR genes, including resistances to aminoglycosides (e.g., alleles of <italic>aac</italic>, <italic>ant</italic>, and <italic>aph</italic>), macrolides [e.g., <italic>erm(A), erm(B)</italic>, and <italic>msrC</italic>], and tetracyclines [e.g., <italic>tet</italic>(K), (L), (M), (O), (S)]. Continuing investigations are required to help understand and mitigate the impact of AR bacteria on human and animal health.</p>