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

In 2011, a novel methicillin resistance gene, mecC, was described in human and bovine Staphylococcus aureus isolates. mecC-positive S. aureus 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 S. aureus isolates containing mecC genes from New Zealand. The two isolates were identified from patients with severe invasion infections as part of an S. aureus bacteraemia study. Whole-genome sequencing was used to characterize staphylococcal cassette chromosome mec (SCCmec) elements and perform phylogenetic comparisons with publicly available strains from mecC-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 SCCmec type XI elements containing a mecC 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 mecC mobile element between the human and hedgehog isolates, indicating the presence of an as-yet-unknown reservoir of mecC S. aureus in the New Zealand environment.