Whole-genome sequencing reveals human to monkey transmission of Staphylococcus aureus in The Gambia and a novel monkey-adapted clade.

Staphylococcus aureus is an important human pathogen that has been shown to occasionally transmit between humans and non-human primates. The frequency and public health implications of these host switches are currently unclear, as are the genomic dynamics underlying host adaptation. Using whole genome sequencing, we infer multiple anthroponotic (human to monkey) transmissions of S. aureus in The Gambia. The observed transmission events resulted in varying degrees of onward transmission in the monkey population and are believed to have occurred over a range of timescales. We report a novel monkey-associated clade of S. aureus likely to have emerged from a human to monkey switch approximately 2,700 years ago. We also report recent anthroponotic transmission of the well-characterised human lineages; ST6 and ST15. By contrast, it appears that zoonotic transmission (from monkeys to humans) is rare. We note a high similarity in accessory-genome content within clonal lineages, and these data imply a contribution from key accessory genome components to host adaptation. We do not consider that monkeys currently constitute a serious risk of S. aureus infection in humans, although as humans encroach further into their natural habitat there is likely to be increased potential for spread in the future.