title: Comparative molecular analysis of community- or hospital-acquired methicillin-resistant Staphylococcus aureus.
abstract: Community-acquired methicillin-resistant Staphylococcus aureus (CA-MRSA) is a growing public health concern that has been associated with pediatric fatalities. It is hypothesized that the evolution of CA-MRSA is a recent event due to the acquisition of mec DNA by previously methicillin-susceptible strains that circulated in the community. This study investigated the genetic relatedness between CA-MRSA, hospital-associated MRSA (HA-MRSA), and nonmenstrual toxic shock syndrome (nmTSS) isolates. Thirty-one of 32 CA-MRSA isolates were highly related as determined by pulsed-field gel electrophoresis and spa typing yet were distinguishable from 32 HA-MRSA strains. The 31 related CA-MRSA isolates produced either staphylococcal enterotoxin B (n = 5) or C (n = 26), and none made TSS toxin 1. All CA-MRSA isolates tested contained a type IV staphylococcal cassette chromosome mec (SCCmec) element. In comparison, none of the HA-MRSA isolates (n = 32) expressed the three superantigens. Antibiotic susceptibility patterns were different between the CA-MRSA and HA-MRSA isolates; CA-MRSA was typically resistant only to beta-lactam antibiotics. Six of twenty-one nmTSS isolates were indistinguishable or highly related to the CA-MRSA isolates. MnCop, an nmTSS isolate obtained in Alabama in 1986, was highly related to the CA-MRSA isolates except that it did not contain an SCCmec element. These data suggest that CA-MRSA strains may represent a new acquisition of SCCmec DNA in a previously susceptible genetic background that was capable of causing nmTSS. CA-MRSA poses a serious health risk not only because it is resistant to the antibiotics of choice for community-acquired staphylococcal infections but also because of its ability to cause nmTSS via superantigen production.
authors.affiliation: Department of Internal Medicine, University of Nebraska Medical Center, Omaha, Nebraska 68198, USA. pfey@unmc.edu
authors.forename: P D
authors.initials: PD
authors.lastname: Fey
authors.forename: B
authors.initials: B
authors.lastname: Saïd-Salim
authors.forename: M E
authors.initials: ME
authors.lastname: Rupp
authors.forename: S H
authors.initials: SH
authors.lastname: Hinrichs
authors.forename: D J
authors.initials: DJ
authors.lastname: Boxrud
authors.forename: C C
authors.initials: CC
authors.lastname: Davis
authors.forename: B N
authors.initials: BN
authors.lastname: Kreiswirth
authors.forename: P M
authors.initials: PM
authors.lastname: Schlievert
mesh_terms: D017714:Community-Acquired Infections / Q000235:genetics*; D003428:Cross Infection / Q000235:genetics*; D016521:Electrophoresis, Gel, Pulsed-Field; D006801:Humans; D007198:Indians, North American / Q000235:genetics*; D016106:Methicillin Resistance / Q000235:genetics*; D009329:Nebraska; D010641:Phenotype; D013211:Staphylococcus aureus / Q000235:genetics* / Q000302:isolation & purification