Genotypic differences between LA-MRSA ST5 and MRSA ST5 from humans with no swine contact

Authors: HAU, SAMANTHA - Iowa State University; ALLUÉ-GUARDIA, ANNA - University Of Texas At San Antonio; RUSCONI, BRIGIDA - University Of Texas At San Antonio; SUN, JISUN - University Of Minnesota; DAVIES, PETER - University Of Minnesota; FRANA, TIMOTHY - Iowa State University; EPPINGER, MARK - University Of Texas At San Antonio; Nicholson, Tracy

Submitted to: American Association of Swine Veterinarians Annual Meeting
Publication Type: Proceedings
Publication Acceptance Date: 1/3/2018
Publication Date: 3/3/2018
Citation: Hau, S.J., Allué-Guardia, A., Rusconi, B., Sun, J., Davies, P.R., Frana, T.S., Eppinger, M., Nicholson, T.L. 2018. Genotypic differences between LA-MRSA ST5 and MRSA ST5 from humans with no swine contact. In: Proceedings of the 49th Annual Meeting of the American Association of Swine Veterinarians, March 3-6, 2018, San Diego, California. p. 57-60.

Interpretive Summary:

Technical Abstract: Introduction Staphylococcus aureus is a commensal bacterium that is found as a component of the microbiota in 25-30% of healthy humans in developed countries.1 Additionally, it causes a range of disease in humans and other species, including skin and soft tissue infections, invasive disease, and toxin mediated disease. Control of S. aureus is complicated by the development of antimicrobial resistance especially methicillin resistance. Methicillin resistant S. aureus (MRSA) isolates have become a significant burden in both the hospital (HA-MRSA) and community settings (CA-MRSA) and are recognized by both the World Health Organization and Centers for Disease Control as a significant drug-resistant threat. More recently, the association of MRSA with swine and other livestock species (LA-MRSA) has raised public health concerns due to the potential that LA-MRSA is contributing to the CA-MRSA burden and livestock may represent the largest source of MRSA outside of hospital settings.2,3 Studies investigating LA-MRSA indicate that many sequence types (STs) are animal adapted, including ST398 and ST9, the most prevalent lineages of LA-MRSA found in swine from Europe and Asia, respectively.4,5 However, this is not the case for MRSA ST5 isolates, which have been reported in swine.6,7 The MRSA ST5 lineage is a globally disseminated cause of both community and hospital acquired infections, leading to additional public health concerns surrounding swine associated LA-MRSA.8 The public health concerns associated with LA-MRSA isolates are two-fold: direct and indirect risks. Direct risks encompass the potential of LA-MRSA to act as a source of infection in humans. Indirect risks of LA-MRSA involve the potential for LA-MRSA isolates act as a source of mobile genetic elements (MGEs) harboring virulence factors or antimicrobial resistance genes that can be transferred to other bacteria. To investigate the potential direct and indirect risks associated with LA-MRSA ST5, we compared a collection of human clinical MRSA ST5 and swine associated LA-MRSA ST5 isolates using genetic analyses and phenotypic screening for antimicrobial resistance and adherence to human keratinocytes and swine skin. Materials and methods Draft genome sequences were generated for 82 LA-MRSA ST5 isolates and 71 clinical MRSA ST5 isolates from humans with no known swine contact using methods previously described.9 Single nucleotide polymorphisms (SNPs) were identified by comparison to the MRSA ST5 reference strain Mu50, as previously described.10 Identified SNPs were utilized in a core genome phylogenetic analysis to detect genome relatedness and included three MRSA ST5 reference strains, two HA-MRSA ST5 isolates (Mu3 and Mu50) and one poultry MRSA ST5 isolate (ED98). Additionally, MGEs encoding antimicrobial resistance genes and virulence factors were detected using online databases including ResFinder and VirulenceFinder and through the use of PCR and BLAST searches of the draft genome sequences.11,12 The information was illustrated using the online tree building tool Evolview.13 Genetic data was paired with phenotypic screening to determine the impact of identified genes. Antimicrobial resistance was evaluated using the microbroth dilution method for antibiotics deemed relevant in the clinical and agricultural setting. Additionally, adherence capacity was evaluated in vitro for both swine skin and human epidermal keratinocytes. Results SNP Identification and Phylogenetic Analysis SNP identification resulted in 759 total SNPs, 245 of which were parsimony informative and utilized for the phylogenetic analysis. Phylogenetic analysis revealed the majority of human clinical MRSA ST5 isolates and swine associated LA-MRSA ST5 isolates clustered into two distinct clades (Figure 1). All but three clinical MRSA ST5 isolates clustered within the clinical MRSA clade, with only one