title: contribution of genetically restricted, methicillin-susceptible strains to the ongoing epidemic of community-acquired Staphylococcus aureus infections.
abstract: BACKGROUND
  Within the current worldwide epidemic of community-acquired Staphylococcus aureus infections, attention has focused on the role of methicillin-resistant strains. We characterize methicillin-susceptible strains that also contribute to this epidemic.
  
  
  METHODS
  We tracked cultures from abscess specimens submitted to the microbiology laboratory at St. Louis Children's Hospital and examined Panton-Valentine leukocidin (PVL) genes in methicillin-susceptible S. aureus (MSSA) isolates. We further characterized some isolates by multilocus sequence typing, pulsed-field gel electrophoresis, antibiotic susceptibility, accessory gene regulator (agr) allele, and presence of the arcA gene of the arginine catabolic mobile element.
  
  
  RESULTS
  From 1999 to 2007, we detected a 250-fold increase in cultures of abscesses yielding methicillin-resistant S. aureus (MRSA) and a 5-fold increase in abscess cultures yielding MSSA. MSSA isolates from abscesses and wounds were more likely to encode PVL than isolates from other sources. In contrast to PVL-negative isolates of MSSA, which were genetically diverse, PVL-positive isolates were predominantly multilocus sequence typing type 8 and agr type 1. More than half of PVL-positive MSSA isolates were resistant to erythromycin and susceptible to clindamycin with the absence of inducible resistance, a pattern uncommon in PVL-negative MSSA but frequent in the USA300 clone of MRSA. In addition, pulsed-field gel electrophoresis of PVL-positive MSSA strains revealed the USA300 pattern.
  
  
  CONCLUSIONS
  In addition to methicillin-resistant strains, the current epidemic of S. aureus infections includes infections caused by methicillin-susceptible strains that are closely related genetically and share phenotypic characteristics other than susceptibility to methicillin. These findings suggest that factors other than methicillin resistance are driving the epidemic.
authors: Department of Pediatrics, Washington University School of Medicine, St. Louis, Missouri 63110, USA.
authors: Rachel C
authors: RC
authors: Orscheln
authors: David A
authors: DA
authors: Hunstad
authors: Stephanie A
authors: SA
authors: Fritz
authors: Jennifer A
authors: JA
authors: Loughman
authors: Kimberly
authors: K
authors: Mitchell
authors: Emily K
authors: EK
authors: Storch
authors: Monique
authors: M
authors: Gaudreault
authors: Patricia L
authors: PL
authors: Sellenriek
authors: Jon R
authors: JR
authors: Armstrong
authors: Elaine R
authors: ER
authors: Mardis
authors: Gregory A
authors: GA
authors: Storch
mesh_terms: D000038:Abscess / Q000453:epidemiology / Q000382:microbiology; D000293:Adolescent; D000818:Animals; D000900:Anti-Bacterial Agents / Q000494:pharmacology; D001426:Bacterial Proteins / Q000235:genetics; D001427:Bacterial Toxins / Q000235:genetics; D015373:Bacterial Typing Techniques / Q000379:methods; D002648:Child; D002675:Child, Preschool; D002981:Clindamycin / Q000494:pharmacology; D016000:Cluster Analysis; D017714:Community-Acquired Infections / Q000453:epidemiology* / Q000382:microbiology*; D016172:DNA Fingerprinting / Q000379:methods; D004269:DNA, Bacterial / Q000235:genetics; D016521:Electrophoresis, Gel, Pulsed-Field; D004917:Erythromycin / Q000494:pharmacology; D005098:Exotoxins / Q000235:genetics; D005260:Female; D005838:Genotype; D006801:Humans; D007956:Leukocidins / Q000235:genetics; D008297:Male; D008712:Methicillin / Q000494:pharmacology; D017422:Sequence Analysis, DNA / Q000379:methods; D013203:Staphylococcal Infections / Q000453:epidemiology* / Q000382:microbiology*; D013211:Staphylococcus aureus / Q000145:classification* / Q000235:genetics / Q000302:isolation & purification*
chemical_list: D000900:Anti-Bacterial Agents; D001426:Bacterial Proteins; D001427:Bacterial Toxins; D004269:DNA, Bacterial; D005098:Exotoxins; D007956:Leukocidins; C078284:Panton-Valentine leukocidin; D002981:Clindamycin; D004917:Erythromycin; D008712:Methicillin