#15-145

Complete

Date Full Report Received

06/23/2016

Date Abstract Report Received

06/23/2016

Investigation

Institution:
Primary Investigator:
Co-Investigators: Tracy Nicholson

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 from one S. aureus bacterial strain to another. Since the gene encoding zinc resistance and the gene encoding methicillin resistance is collocated 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 from pigs. In this study we identified the prevalence of the czrC gene and phenotypic zinc resistance in US swine associated LA-MRSA ST5 isolates, MRSA ST5 isolates from humans with no swine contact, and US swine associated LA-MRSA ST398 isolates. Our data demonstrate that the prevalence of zinc resistance in US swine associated LA-MRSA ST5 isolates was significantly lower than the prevalence of zinc resistance in MRSA ST5 isolates from humans with no swine contact, swine associated LA-MRSA ST398 isolates, and previous reports describing zinc resistance in other LA-MRSA ST398 isolates. Collectively our data suggests selection pressure 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.
Contact Information:
Tracy L. Nicholson, Ph.D.
National Animal Disease Center, ARS, USDA
1920 Dayton Ave.
Ames, Iowa 50010
Telephone: +1 515 337 7349
E-mail: tracy.nicholson@ARS.USDA.GOV