Most clonal lineages of Staphylococcus epidermidis are commensals present on human skin and in the nose. However, some globally spreading healthcare-associated and methicillin-resistant S. epidermidis (HA-MRSE) clones are major causes of difficult-to-treat implant or bloodstream infections. The molecular determinants that alter the lifestyle of S. epidermidis have remained elusive, and their identification might provide therapeutic targets. We reasoned that changes in surface-exposed wall teichoic acid (WTA) polymers of S. epidermidis, which potentially shape host interactions, may be linked to differences between colonization and infection abilities of different clones. We used a combined epidemiological and functional approach to show that while commensal clones express poly-glycerolphosphate WTA, S. epidermidis multilocus sequence type 23, which emerged in the past 15 years and is one of the main infection-causing HA-MRSE clones, contains an accessory genetic element, tarIJLM, that leads to the production of a second, Staphylococcus aureus-type WTA (poly-ribitolphosphate (RboP)). Production of RboP-WTA by S. epidermidis impaired in vivo colonization but augmented endothelial attachment and host mortality in a mouse sepsis model. tarIJLM was absent from commensal human sequence types but was found in several other HA-MRSE clones. Moreover, RboP-WTA enabled S. epidermidis to exchange DNA with S. aureus via siphovirus bacteriophages, thereby creating a possible route for the inter-species exchange of methicillin resistance, virulence and colonization factors. We conclude that tarIJLM alters the lifestyle of S. epidermidis from commensal to pathogenic and propose that RboP-WTA might be a robust target for preventive and therapeutic interventions against MRSE infections.

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