Assessing vancomycin and teicoplanin minimal inhibitory concentrations (MICs) among clinical isolates of oxacillin-resistant Staphylococcus aureus in Brazil: is glycopeptide "creep" present among Brazilian isolates?

• Grant number: 09/15986-3
• Support Opportunities: Regular Research Grants
• Start date: March 01, 2010
• End date: February 29, 2012
• Field of knowledge: Health Sciences - Medicine - Medical Clinics
• Principal Investigator: Ana Cristina Gales
• Grantee: Ana Cristina Gales
• Host Institution: Escola Paulista de Medicina (EPM). Universidade Federal de São Paulo (UNIFESP). Campus São Paulo. São Paulo , SP, Brazil

Abstract

Vancomycin treatment failure in methicillin-resistant S. aureus (ORSA) infections has been described, especially associated with increased vancomycin MICs (>1 µg/mL). Vancomycin "MIC creep" is defined as a trend towards higher vancomycin MIC results for clinical isolates of S. aureus. Studies reporting vancomycin MIC creep for ORSA have produced conflicting results: some institutions have reported MIC creep, but some multicenter surveillance studies have not demonstrated these phenomena. Moreover, these studies were conducted predominantly in the United States, where teicoplanin is not prescribed for treatment of ORSA infections and the Brazilian epidemic ORSA clone is not prevalent. The lack of regional and worldwide data on "teicoplanin MIC creep" does not allow the affirmation that vancomycin MIC creep will be accompanied by increasing teicoplanin MICs. Such data are needed in Brazil to clarify if gradual increases on either teicoplanin or vancomycin MICs are occurring among the local ORSA bacterial population. Methods: This study will be conducted at Laboratório Alerta - Universidade Federal de São Paulo. A total of 200 bacterial isolates of ORSA will be included, collected from patients admitted at Hospital São Paulo from 2002-2009 (25 per year, only one per patient). Isolates will be representative of clinically significant bloodstream infections. Minimum inhibitory concentration values will be determined by Etest and also by Clinical and Laboratory Standards Institute (CLSI, 2009) broth microdilution method for vancomycin and teicoplanin. Thirty-sic dilutions between 0.06 and 64 ¼g/ml will be tested for both glycopeptides. Results will be analyzed as: i) yearly variations on the central tendency of MICs (mode) and ii) yearly geometric mean MIC results. All isolates will be genetically typed by pulsed-field gel electrophoresis, in order to exclude increase in the glycopeptide MIC due to spread of an endemic clone. (AU)