Antimicrobial resistance distribution among methicillin resistant Staphylococcus aureus sequence type (ST) 5 isolates from health care and agricultural sources

Authors: HAU, SAMANTHA - Iowa State University; HAAN, JISUN - University Of Minnesota; DAVIES, PETER - University Of Minnesota; FRANA, TIMOTHY - Iowa State University; Nicholson, Tracy

Submitted to: Frontiers in Microbiology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 8/17/2018
Publication Date: 9/11/2018
Citation: Hau, S.J., Haan, J.S., Davies, P.R., Frana, T., Nicholson, T.L. 2018. Antimicrobial resistance distribution differs among methicillin resistant Staphylococcus aureus sequence type (ST) 5 isolates from health care and agricultural sources. Frontiers in Microbiology. 9:2102. https://doi.org/10.3389/fmicb.2018.02102.
DOI: https://doi.org/10.3389/fmicb.2018.02102

Interpretive Summary: Livestock-associated methicillin-resistant Staphylococcus aureus (LA-MRSA) draws concern from the public health community for two main reasons. The first reason is that these isolates are the single largest reservoir of MRSA outside of hospital settings and secondly, similar to all MRSA strains, LA-MRSA strains tend to contain a high number of antimicrobial resistance (AMR) genes. In the US, a diverse population of LA-MRSA is found including organisms of the sequence type (ST) 398, ST9, and ST5 lineages. Occurrence of ST5 MRSA in swine has raised additional public health concerns because ST5 is a highly successful and globally disseminated MRSA lineage in humans reaching pandemic levels. In this report we determined the phenotypic antimicrobial susceptibilities and genotypic mechanisms of antimicrobial resistance among swine associated LA-MRSA ST5 and clinical MRSA ST5 isolates. Swine associated LA-MRSA ST5 isolates exhibited resistance to fewer antibiotics than clinical MRSA ST5 isolates from humans with no swine contact. Additionally, we found the phenotypic antimicrobial susceptibilities and genotypic mechanisms of antimicrobial resistance among swine associated LA-MRSA ST5 and clinical MRSA ST5 isolates to be separate and distinct, suggesting that MRSA isolates from agricultural sources are not currently acting as a source of antimicrobial resistance elements for clinical human MRSA isolates.

Technical Abstract: Antimicrobial resistance is a growing issue in bacteria and methicillin resistant Staphylococcus aureus (MRSA) is a notable example. Since the discovery of livestock associated MRSA (LA-MRSA), public health concerns have arisen surrounding the potential of LA-MRSA isolates to serve as a reservoir for antimicrobial resistance determinants. In this study, we compare swine associated LA-MRSA ST5 and human clinical MRSA ST5 isolates for phenotypic antimicrobial susceptibilities determined via microbroth dilution and genotypic determinants of antimicrobial resistance using whole genome sequencing and comparative genomic analysis to identify antimicrobial resistance elements. Swine associated LA-MRSA ST5 isolates exhibited resistance to fewer antibiotics than clinical MRSA ST5 isolates from humans with no swine contact. Distinct genomic antimicrobial resistance elements were harbored by each subgroup, with little overlap in shared antimicrobial resistance genes between swine associated LA-MRSA ST5 and clinical MRSA ST5 isolates. Our results demonstrate that phenotypic antimicrobial susceptibilities and genotypic determinants of antimicrobial resistance among swine associated LA-MRSA ST5 and clinical MRSA ST5 isolates are separate and distinct suggesting that ST5 MRSA isolates from agricultural sources were not a source of antimicrobial resistance elements for these clinical human ST5 MRSA isolates.