Methicillin-Resistant Staphylococcus aureus Adaptation to Human

ABSTRACT Skin is the most common site of Staphylococcus aureus infection. While most of these infections are self-limited, re-current infections are common. Keratinocytes and recruited immune cells participate in skin defense against infection. We pos-tulated that S. aureus is able to adapt to the milieu within human keratinocytes to avoid keratinocyte-mediated clearance. From a collection of S. aureus isolated from chronically infected patients with atopic dermatitis, we noted 22 % had an agrmutant-like phenotype. Using several models of human skin infection, we demonstrate that toxin-deficient, agrmutants of methicillin-resistant S. aureus (MRSA) USA300 are able to persist within keratinocytes by stimulating autophagy and evading caspase-1 and inflammasome activation. MRSA infection induced keratinocyte autophagy, as evidenced by galectin-8 and LC3 accumulation. Autophagy promoted the degradation of inflammasome components and facilitated staphylococcal survival. The recovery of more than 58 % agr or RNAIII mutants (P< 0.0001) of an inoculum of wild-type (WT)MRSA fromwithin wortmannin-treated keratinocytes compared to control keratinocytes reflected the survival advantage for mutants no longer expressing agr-dependent toxins. Our results illustrate the dynamic interplay between S. aureus and keratinocytes that can result in the selec-tion of mutants that have adapted specifically to evade keratinocyte-mediated clearance mechanisms. IMPORTANCE Human skin is a major site of staphylococcal infection, and keratinocytes actively participate in eradication of these pathogens. We demonstrate that methicillin-resistant Staphylococcus aureus (MRSA) is ingested by keratinocytes and acti-vates caspase-1-mediated clearance through pyroptosis. Toxin-deficient MRSAmutants are selected within keratinocytes tha