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ARS Home » Midwest Area » Ames, Iowa » National Animal Disease Center » Virus and Prion Research » Research » Publications at this Location » Publication #328583
Title: Zinc resistance within swine associated methicillin resistant Staphylococcus aureus (MRSA) isolates in the USA is associated with MLST lineage

Author
item HAU, SAMANTHA - Iowa State University
item FRANA, TIMOTHY - Iowa State University
item SUN, JISUN - University Of Minnesota
item DAVIES, PETER - University Of Minnesota
item Nicholson, Tracy

Submitted to: Applied and Environmental Microbiology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 5/7/2017
Publication Date: 5/19/2017
Citation: Hau, S.J., Frana, T.S., Sun, J., Davies, P.R., Nicholson, T.L. 2017. Zinc resistance within swine associated methicillin resistant Staphylococcus aureus (MRSA) isolates in the USA is associated with MLST lineage. Applied and Environmental Microbiology. pii: AEM.00756-17. doi: 10.1128/AEM.00756-17.

Interpretive Summary: Livestock associated methicillin-resistant Staphylococcus aureus (LA-MRSA) draws concern from the public health community because in some countries these organisms may represent the largest reservoir of MRSA outside hospital settings. The emergence and prevalence of LA-MRSA sequence type (ST) 398 isolates in Europe has been attributed in part to the in feed use of zinc as an antidiarrheal agent. The gene encoding zinc resistance is located on the same segment of DNA that also contains the gene encoding resistance to the antibiotic methicillin. This segment of DNA is referred to as the staphylococcal cassette chromosome mec (SCCmec) element and it is easily transferred or spread from one S. aureus bacterial strain to another. Since the gene encoding zinc resistance and the gene encoding methicillin resistance are co-located on the SCCmec element, it has been suggested that the use of in feed zinc as an antimicrobial has the potential to contribute to the emergence and spread of MRSA in swine by increasing the selective pressure to maintain the SCCmec element in isolates obtained from pigs. In this study we report the prevalence of zinc resistance in US swine associated LA-MRSA ST5 isolates, MRSA ST5 isolates from humans with no swine contact, and LA-MRSA ST398 isolates. We demonstrate that the prevalence of zinc resistance in US swine associated LA-MRSA ST5 isolates is significantly less than the prevalence of zinc resistance in both MRSA ST5 isolates from humans with no swine contact and LA-MRSA ST398 isolates, as well as previously reported zinc resistance in other LA-MRSA ST398 isolates. Collectively our data suggest that co-selection thought to be associated with application of zinc in feed is not playing a role in the prevalence and persistence of LA-MRSA ST5 in the US swine population. Additionally, our data indicate that zinc resistance is more associated with MLST lineage suggesting a potential link between genetic lineage and carriage of an antimicrobial resistance gene.

Technical Abstract: Zinc resistance in livestock-associated methicillin resistant Staphylococcus aureus (LA-MRSA) is mediated by the czrC gene co-located with the mecA gene, encoding methicillin resistance, on the type V SCCmec element. Since the czrC gene and the mecA gene are co-located on the SCCmec element, it has been suggested that the use of in feed zinc as an antimicrobial has the potential to contribute to the emergence and spread of MRSA in swine by increasing the selective pressure to maintain the SCCmec element in isolates obtained from pigs. In this study we report the prevalence of zinc resistance in US swine associated LA-MRSA ST5 isolates, MRSA ST5 isolates from humans with no swine contact, and LA-MRSA ST398 isolates. We demonstrate that the prevalence of zinc resistance in US swine associated LA-MRSA ST5 isolates is significantly less than the prevalence of zinc resistance in both MRSA ST5 isolates from humans with no swine contact and LA-MRSA ST398 isolates, as well as previously reported zinc resistance in other LA-MRSA ST398 isolates. Collectively our data suggest that co-selection thought to be associated with application of zinc in feed is not playing a role in the prevalence and persistence of LA-MRSA ST5 in the US swine population. Additionally, our data indicate that zinc resistance is more associated with MLST lineage suggesting a potential link between genetic lineage and carriage of resistance markers.