title: PSMs of hypervirulent Staphylococcus aureus act as intracellular toxins that kill infected osteoblasts.
abstract: Epidemic community-acquired methicillin-resistant Staphylococcus aureus (CA-MRSA) is associated with more severe and acute forms of osteomyelitis than healthcare-associated (HA-) MRSA. Although S. aureus is now recognized as a facultative intracellular pathogen, the contribution of osteoblast invasion by CA-MRSA to the pathogenesis of osteomyelitis is unknown. Using an ex vivo model of intracellular infection of human osteoblasts, we demonstrated that CA-MRSA strains of diverse lineages share an enhanced ability to kill infected osteoblasts compared to HA-MRSA. Cytotoxicity comparisons of CA-MRSA isogenic deletion mutants revealed that phenol-soluble modulins (PSMs), a class of membrane-damaging exoproteins that are expressed at higher levels in CA-MRSA than in HA-MRSA, are involved in this osteoblast killing, whereas other major CA-MRSA virulence determinants, the Panton-Valentine leukocidin and alpha-toxin, are not involved. Similarly, functional agr and sarA regulators, which control the expression of PSMs and alpha-toxin, were required for the expression of the intracellular cytotoxic phenotype by CA-MRSA, whereas the saeRS regulator, which controls the expression of alpha-toxin but not PSMs, had no impact on cytotoxicity. Finally, PSM transcript levels determined by quantitative reverse-transcriptase PCR were significantly higher in CA-MRSA than in HA-MRSA strains and associated with cell damage in MRSA-infected osteoblasts. These findings provide new insights into the pathogenesis of severe CA-MRSA osteomyelitis and unravel a novel virulence strategy of CA-MRSA, based on the invasion and subsequent killing of osteoblasts by PSMs acting as intracellular toxins.
authors.affiliation: Institut National de la Santé et de la Recherche Médicale (INSERM) U1111, University of Lyon, Lyon, France.
authors.forename: Jean-Philippe
authors.initials: JP
authors.lastname: Rasigade
authors.forename: Sophie
authors.initials: S
authors.lastname: Trouillet-Assant
authors.forename: Tristan
authors.initials: T
authors.lastname: Ferry
authors.forename: Binh An
authors.initials: BA
authors.lastname: Diep
authors.forename: Anaïs
authors.initials: A
authors.lastname: Sapin
authors.forename: Yannick
authors.initials: Y
authors.lastname: Lhoste
authors.forename: Jérémy
authors.initials: J
authors.lastname: Ranfaing
authors.forename: Cédric
authors.initials: C
authors.lastname: Badiou
authors.forename: Yvonne
authors.initials: Y
authors.lastname: Benito
authors.forename: Michèle
authors.initials: M
authors.lastname: Bes
authors.forename: Florence
authors.initials: F
authors.lastname: Couzon
authors.forename: Sylvestre
authors.initials: S
authors.lastname: Tigaud
authors.forename: Gérard
authors.initials: G
authors.lastname: Lina
authors.forename: Jérôme
authors.initials: J
authors.lastname: Etienne
authors.forename: François
authors.initials: F
authors.lastname: Vandenesch
authors.forename: Frédéric
authors.initials: F
authors.lastname: Laurent
mesh_terms: D058491:Bacterial Load; D001427:Bacterial Toxins / Q000633:toxicity*; D016923:Cell Death / Q000187:drug effects; D017714:Community-Acquired Infections / Q000382:microbiology; D003695:Delivery of Health Care; D015964:Gene Expression Regulation, Bacterial; D006801:Humans; D042541:Intracellular Space / Q000187:drug effects* / Q000382:microbiology*; D055624:Methicillin-Resistant Staphylococcus aureus / Q000502:physiology*; D010006:Osteoblasts / Q000166:cytology* / Q000187:drug effects / Q000382:microbiology*; D012333:RNA, Messenger / Q000235:genetics / Q000378:metabolism; D013045:Species Specificity
chemical_list: D001427:Bacterial Toxins; D012333:RNA, Messenger; C025971:staphylococcal delta toxin