title: [Methicillin resistance and vancomycin susceptibility pattern among blood isolates of Staphylococcus aureus].
abstract: BACKGROUND
  Staphylococcus aureus is capable of acquiring resistance against all antimicrobial agents. Vancomycin has been the cornerstone therapy for serious methicillin-resistant S. aureus infections. However, vancomycin treatment failures have been reported.
  
  
  METHODS
  From March to August 2010, S. aureus blood isolates were included to determine methicillin-resistance and the vancomycin susceptibility by using a standard microdilution method. To detect methicillin-resistance, a Mueller-Hinton agar plate added with oxacillin 4 µg/mL and 2 % NaCl, and an agglutination test were used. Growth of S. aureus on the agar plate and/or reactive agglutination defined a methicillin-resistant organism. Vancomycin susceptibility was assessed by determining the minimal inhibitory concentration (MIC) in Muelller-Hinton agar plates prepared with dilutions ranging from 16 to 0.5 µg/mL.
  
  
  RESULTS
  A total of 25 blood-isolates of S. aureus were included. A 60 % was methicillin-resistant. All isolates were vancomycin-susceptible (MIC ≤ 2 µg/mL) showing the next MICs distribution: 48 % ≤ 0.5 µg/mL; 44 % 1 µg/mL, and 8 % 2 µg/mL.
  
  
  CONCLUSIONS
  The high proportion of methicillin-resistance among S. aureus and the presence of vancomycin susceptible phenotypes (MIC of 2 µg/mL) not only claim for an enforcement of standard precautions and antimicrobial control, but also for a regular surveillance of vancomycin susceptibility pattern using a reference method.
authors.affiliation: Servicio de Infectología Adultos, Hospital de Infectología, Centro Médico Nacional La Raza, Instituto Mexicano del Seguro Social, Distrito Federal, México. elena_urdez_hdz@yahoo.com.mx.
authors.forename: Jonathan
authors.initials: J
authors.lastname: Rodríguez-Pineda
authors.forename: José Juan
authors.initials: JJ
authors.lastname: Terrazas-Estrada
authors.forename: Elena
authors.initials: E
authors.lastname: Urdez-Hernández
authors.forename: Eva Aurora
authors.initials: EA
authors.lastname: Hernández-Sánchez
authors.forename: Sandra Leticia
authors.initials: SL
authors.lastname: Sánchez-Tejeda
mesh_terms: D006779:Hospitals, Public; D016106:Methicillin Resistance; D055624:Methicillin-Resistant Staphylococcus aureus / Q000187:drug effects* / Q000302:isolation & purification; D008800:Mexico; D008826:Microbial Sensitivity Tests; D020713:Vancomycin Resistance
keywords: Methicillin resistant Staphylococcus aureus; Vancomycin resistance