title: Methicillin-resistant Staphylococcus aureus adaptation to human keratinocytes.
abstract: Skin is the most common site of Staphylococcus aureus infection. While most of these infections are self-limited, recurrent infections are common. Keratinocytes and recruited immune cells participate in skin defense against infection. We postulated 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 agr mutant-like phenotype. Using several models of human skin infection, we demonstrate that toxin-deficient, agr mutants 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 from within 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 selection of mutants that have adapted specifically to evade keratinocyte-mediated clearance mechanisms.
  
  
  OBJECTIVE
  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 activates caspase-1-mediated clearance through pyroptosis. Toxin-deficient MRSA mutants are selected within keratinocytes that fail to induce caspase-1 activity and keratinocyte-mediated clearance. These intracellular staphylococci induce autophagy that enhances their intracellular survival by diminishing inflammasome components. These findings suggest that S. aureus mutants, by exploiting autophagy, can persist within human keratinocytes.
authors.affiliation: Department of Pediatrics, College of Physicians & Surgeons, Columbia University, New York, New York, USA.
authors.forename: Grace
authors.initials: G
authors.lastname: Soong
authors.affiliation: Department of Pediatrics, College of Physicians & Surgeons, Columbia University, New York, New York, USA.
authors.forename: Franklin
authors.initials: F
authors.lastname: Paulino
authors.affiliation: Department of Pediatrics, College of Physicians & Surgeons, Columbia University, New York, New York, USA.
authors.forename: Sarah
authors.initials: S
authors.lastname: Wachtel
authors.affiliation: Department of Pediatrics, College of Physicians & Surgeons, Columbia University, New York, New York, USA.
authors.forename: Dane
authors.initials: D
authors.lastname: Parker
authors.affiliation: Department of Pediatrics, College of Physicians & Surgeons, Columbia University, New York, New York, USA.
authors.forename: Matthew
authors.initials: M
authors.lastname: Wickersham
authors.affiliation: Department of Pediatrics, College of Physicians & Surgeons, Columbia University, New York, New York, USA.
authors.forename: Dongni
authors.initials: D
authors.lastname: Zhang
authors.affiliation: Department of Pediatrics, College of Physicians & Surgeons, Columbia University, New York, New York, USA.
authors.forename: Armand
authors.initials: A
authors.lastname: Brown
authors.affiliation: Department of Dermatology, College of Physicians & Surgeons, Columbia University, New York, New York, USA.
authors.forename: Christine
authors.initials: C
authors.lastname: Lauren
authors.affiliation: Department of Pediatrics, College of Physicians & Surgeons, Columbia University, New York, New York, USA.
authors.forename: Margaret
authors.initials: M
authors.lastname: Dowd
authors.affiliation: Department of Pediatrics, College of Physicians & Surgeons, Columbia University, New York, New York, USA.
authors.forename: Emily
authors.initials: E
authors.lastname: West
authors.affiliation: Department of Dermatology, College of Physicians & Surgeons, Columbia University, New York, New York, USA.
authors.forename: Basil
authors.initials: B
authors.lastname: Horst
authors.affiliation: Department of Pediatrics, College of Physicians & Surgeons, Columbia University, New York, New York, USA.
authors.forename: Paul
authors.initials: P
authors.lastname: Planet
authors.affiliation: Department of Pediatrics, College of Physicians & Surgeons, Columbia University, New York, New York, USA asp7@columbia.edu.
authors.forename: Alice
authors.initials: A
authors.lastname: Prince
mesh_terms: D000220:Adaptation, Biological; D000818:Animals; D001343:Autophagy; D001426:Bacterial Proteins; D001427:Bacterial Toxins / Q000378:metabolism; D006801:Humans; D057131:Immune Evasion; D015603:Keratinocytes / Q000382:microbiology*; D055624:Methicillin-Resistant Staphylococcus aureus / Q000502:physiology*; D051379:Mice; D015534:Trans-Activators / Q000172:deficiency
chemical_list: C095698:Agr protein, Staphylococcus aureus; D001426:Bacterial Proteins; D001427:Bacterial Toxins; D015534:Trans-Activators