Genomic epidemiology of mecC-carrying Staphylococcus aureus isolates from human clinical cases in New Zealand

In 2011, a novel methicillin resistance gene, <i>mecC</i>, was described in human and bovine <i>Staphylococcus aureus</i> isolates. <i>mecC-</i>positive <i>S. aureus</i> is most commonly associated with livestock and wildlife populations across Europe and is particularly prevalent in hedgehogs, but only occasionally causes human infections. In this study, we characterize and investigate the origin of two human <i>S. aureus</i> isolates containing <i>mecC</i> genes from New Zealand. The two isolates were identified from patients with severe invasion infections as part of an <i>S. aureus</i> bacteraemia study. Whole-genome sequencing was used to characterize staphylococcal cassette chromosome <i>mec</i> (SCC<i>mec</i>) elements and perform phylogenetic comparisons with publicly available strains from <i>mecC</i>-associated clonal complexes, including isolates from hedgehogs from New Zealand and Europe/United Kingdom (UK), and livestock, wildlife and human isolates from Europe/UK. The two isolates from our study have almost identical SCC<i>mec</i> type XI elements containing a <i>mecC</i> gene. However, this gene contains a premature stop codon, consistent with the methicillin-susceptible phenotype observed for these isolates. Core genome SNP analyses showed that the two isolates are 234 SNPs apart and are most closely related to an isolate obtained from a New Zealand hedgehog. However, there are considerable differences in the <i>mecC</i> mobile element between the human and hedgehog isolates, indicating the presence of an as-yet-unknown reservoir of <i>mecC S. aureus</i> in the New Zealand environment.