UNLABELLED

Methicillin resistance in is conferred by the mobile genetic element, staphylococcal cassette chromosome (SCC). Methicillin-resistant (MRSA) can transmit among animals and humans, leading to persistence and back transmission events. The current study tested the hypothesis that companion animal and livestock-associated (LA) MRSA isolates share genomic similarity, suggesting shared ancestry with hospital-associated (HA) or community-associated (CA) MRSA. Eight . isolates from therapy dogs ( = 5) and bulk tank milk ( = 3) were genome sequenced, and 71,721 genome-wide single nucleotide polymorphism (SNP) locations were extracted and phylogenetically compared against methicillin-sensitive (MSSA) and MRSA genomes of isolates from a variety of species and time frames, available in the National Center for Biotechnology Information (NCBI) database. A maximum likelihood phylogenetic tree was constructed to define lineages across isolates from animals and humans. Four isolates from companion animals and three bulk tank milk isolates clustered with human isolates, while one companion animal isolate clustered with genomes of MRSA isolated from swine. Four therapy dog isolates had CA-MRSA SCC types IVa, IVc, and V/VII, respectively, while one therapy dog and one bulk tank milk isolate shared SCC type (IIa) that is commonly seen in HA-MRSA. Two isolates from bulk tank milk were methicillin sensitive and did not carry .

IMPORTANCE

Methicillin-resistant (MRSA) infections are a major medical concern, causing a range of conditions from skin infections and invasive disease to death. MRSA was discovered as a nosocomial infection; however, it has since been isolated in communities and animals worldwide. This research was significant because canine and bulk tank milk isolates were found to have genomic relatedness to human and domestic animal isolates. This genetic relatedness implies either a parallel evolution within hosts converging to successful genotypes or real interspecies transmission events among animals and humans.