title: [Decreasing susceptibility to vancomycin in isogenic Staphylococcus aureus strains isolated from a single patient].
abstract: BACKGROUND
  We aimed at evaluating the microbiological characteristics and clinical implication of 7 isogenic strains of Staphylococcus aureus with decreased susceptibility to vancomycin.
  
  
  METHODS
  A patient with nosocomial trival vularendocarditis due to methicillin-resistant S. aureus had positive blood cultures for 8 weeks despite antimicrobial therapy with vancomycin (normal serum levels) and rifampicin. The patient rejected surgical treatment but the process cured with antimicrobial therapy. The epidemiological relationship of strains was evaluated by pulsed field gel electrophoresis. The susceptibility to vancomycin was evaluated by microdilution and E-test using two different in ocula. The activity of oxacillin, ampicillin and cephalotin was evaluated in Mueller Hinton (MH) agar containing different concentrations of vancomycin (0.06 to 4 mg/l). Heteroresistant subpopulations were determined in both MH and brain heart infussion agar containing vancomycin (0.5 to 512 mg/l). All seven strains belonged to the same clone. Vancomycin MIC ranged from 1 mg/l (isolates 1 to 5) to 4 mg/l (isolates 6 and 7). Isolates 6 and 7 displayed differences in pigmentation and slower growth rates. The susceptibility of these isolates to betalactams inMH containing different concentrations of vancomycin was greater than that in controls. Subpopulations heteroresistant to vancomycin were not detected.
  
  
  CONCLUSIONS
  The decreased susceptibility of the isogenic S. aureus strains evaluated in this study was not due to heteroresistance and did not cause therapeutic failure.
authors.affiliation: Departamento de Microbiología, Hospital Universitario Virgen Macarena, Sevilla, Spain.
authors.lastname: Pascual A
authors.forename: J
authors.initials: J
authors.lastname: Rodríguez-Baño
authors.forename: E
authors.initials: E
authors.lastname: Ramírez De Arellano
authors.forename: J
authors.initials: J
authors.lastname: Mola
authors.forename: L
authors.initials: L
authors.lastname: Martínez-Martínez
mesh_terms: D000368:Aged; D000900:Anti-Bacterial Agents / Q000494:pharmacology*; D004351:Drug Resistance; D006801:Humans; D008297:Male; D013211:Staphylococcus aureus / Q000187:drug effects* / Q000302:isolation & purification; D014640:Vancomycin / Q000494:pharmacology*
chemical_list: D000900:Anti-Bacterial Agents; D014640:Vancomycin
vernacular_title: Sensibilidad disminuida a vancomicina en cepas isogénicas de Staphylococcus aureus aisladas del mismo paciente.