RESUMO
BACKGROUND: The predominant genetic background of community-associated methicillin-resistant Staphylococcus aureus has transitioned from USA400 to USA300 in most US communities. The explanation for this shift is unclear. We hypothesized that USA300 must be more pathogenic--specifically, that USA300 would have increased virulence when compared with USA400 in an animal model. METHODS: Rats were inoculated intratracheally with 1 of 6 S. aureus isolates from the USA300 and USA400 backgrounds. We assessed mortality, in vivo bacterial growth, and histopathology. We assessed the in vitro expression of capsule and of selected genes believed to be important in virulence in S. aureus, including agr, saeRS, sarA, alpha-toxin (hla), and Panton-Valentine leukocidin (pvl). RESULTS: USA300 isolates were more lethal, produced more severe pneumonia, and had higher in vivo bacterial density in the lung than did USA400 isolates. In vitro expression of agr, saeRS, sarA, hla, and pvl were greater in USA300 isolates. USA300 isolates were unencapsulated, whereas 2 of 3 USA400 isolates produced capsule. CONCLUSIONS: USA300 isolates were more virulent than USA400 isolates in a model of necrotizing pneumonia. The explanation for this is unclear, but it likely results from increased expression of S. aureus regulatory systems (e.g., agr, saeRS, and sarA) and the resultant upregulation of key virulence factors including alpha-toxin and PVL.
Assuntos
Toxinas Bacterianas/genética , Infecções Comunitárias Adquiridas/microbiologia , Resistência a Meticilina , Infecções Estafilocócicas/microbiologia , Staphylococcus aureus/patogenicidade , Animais , Toxinas Bacterianas/biossíntese , Infecções Comunitárias Adquiridas/epidemiologia , Infecções Comunitárias Adquiridas/fisiopatologia , Modelos Animais de Doenças , Exotoxinas/biossíntese , Leucocidinas/biossíntese , Pneumonia Estafilocócica/fisiopatologia , Ratos , Infecções Estafilocócicas/epidemiologia , Infecções Estafilocócicas/fisiopatologia , Staphylococcus aureus/classificação , Staphylococcus aureus/genética , Virulência , Fatores de VirulênciaRESUMO
The agr specificity group distribution of persistent Staphylococcus aureus clones recovered from the airways of cystic fibrosis (CF) patients did not differ from that of isolates recovered from various clinical infections and healthy nasal carriers. The success of CF clones in terms of cocolonization and/or infection with S. aureus, prevalence of clones, or persistence appeared to be independent of agr group specificity.
