title: Vancomycin modifies the expression of the agr system in multidrug-resistant Staphylococcus aureus clinical isolates.
abstract: Staphylococcus aureus is an opportunistic pathogen that colonizes human hosts and causes a wide variety of diseases. Two interacting regulatory systems called agr (accessory gene regulator) and sar (staphylococcal accessory regulator) are involved in the regulation of virulence factors. The aim of this study was to evaluate the effect of vancomycin on hld and spa gene expression during the exponential and post-exponential growth phases in multidrug-resistant (MDR) S. aureus.
  
  
  METHODS
  Antibiotic susceptibility was evaluated by the standard microdilution method. The phylogenetic profile was obtained by pulsed-field gel electrophoresis (PFGE). Polymorphisms of agr and SCCmec (staphylococcal cassette chromosome mec) were analyzed by multiplex polymerase chain reaction (PCR). The expression levels of hld and spa were analyzed by reverse transcription-PCR. An enzyme-linked immunosorbent assay (ELISA) was performed to detect protein A, and biofilm formation was analyzed via crystal violet staining.
  
  
  RESULTS
  In total, 60.60% (20/33) of S. aureus clinical isolates were MDR. Half (10/20) of the MDR S. aureus isolates were distributed in subcluster 10, with >90% similarity among them. In the isolates of this subcluster, a high prevalence (100%) for the agrII and the cassette SCCmec II polymorphisms was found. Our data showed significant increases in hld expression during the post-exponential phase in the presence and absence of vancomycin. Significant increases in spa expression, protein A production and biofilm formation were observed during the post-exponential phase when the MDR S. aureus isolates were challenged with vancomycin.
  
  
  CONCLUSIONS
  The polymorphism agrII, which is associated with nosocomial isolates, was the most prevalent polymorphism in MDR S. aureus. Additionally, under our study conditions, vancomycin modified hld and spa expression in these clinical isolates. Therefore, vancomycin may regulate alternative systems that jointly participate in the regulation of these virulence factors.
authors.affiliation: Laboratorio de Investigación en Bacteriología Intestinal, Hospital Infantil de México Federico Gómez México DF, Mexico.
authors.forename: Vicenta
authors.initials: V
authors.lastname: Cázares-Domínguez
authors.affiliation: Laboratorio de Investigación en Bacteriología Intestinal, Hospital Infantil de México Federico Gómez México DF, Mexico.
authors.forename: Sara A
authors.initials: SA
authors.lastname: Ochoa
authors.affiliation: Laboratorio de Investigación en Bacteriología Intestinal, Hospital Infantil de México Federico Gómez México DF, Mexico.
authors.forename: Ariadnna
authors.initials: A
authors.lastname: Cruz-Córdova
authors.affiliation: Laboratorio de Investigación en Bacteriología Intestinal, Hospital Infantil de México Federico Gómez México DF, Mexico.
authors.forename: Gerardo E
authors.initials: GE
authors.lastname: Rodea
authors.affiliation: Laboratorio de Investigación en Bacteriología Intestinal, Hospital Infantil de México Federico Gómez México DF, Mexico.
authors.forename: Gerardo
authors.initials: G
authors.lastname: Escalona
authors.affiliation: Laboratorio de Infectología, Hospital Infantil de México Federico Gómez México DF, Mexico.
authors.forename: Alma L
authors.initials: AL
authors.lastname: Olivares
authors.affiliation: Posgrado en Ciencias Genómicas, Universidad Autónoma de la Ciudad de México México DF, Mexico.
authors.forename: José de Jesús
authors.initials: Jde J
authors.lastname: Olivares-Trejo
authors.affiliation: Laboratorio de Infectología, Hospital Infantil de México Federico Gómez México DF, Mexico.
authors.forename: Norma
authors.initials: N
authors.lastname: Velázquez-Guadarrama
authors.affiliation: Laboratorio de Investigación en Bacteriología Intestinal, Hospital Infantil de México Federico Gómez México DF, Mexico.
authors.forename: Juan
authors.initials: J
authors.lastname: Xicohtencatl-Cortes
keywords: Staphylococcus aureus; agr system; antibiotics; multidrug-resistant; vancomycin