INVESTIGADORES
MOLLERACH Marta Eugenia
congresos y reuniones científicas
Título:
Methicillin resistance and Vancomycin reduced susceptibility in Staphylococcus aureus: a hidden link?
Autor/es:
DI GREGORIO S; CUIROLO A; GARDELLA N; FERNÁNDEZ S; FAMIGLIETTI A; AMOROSO A; JORIS B; MOLLERACH M
Reunión:
Congreso; 6th International Conference on Gram-Positive Microorganisms; 2011
Institución organizadora:
The Scripps Research Institute
Resumen:
Vancomycin is currently the treatment of choice for serious infectious caused by methicillin resistant Staphylococcus aureus (MRSA), but several cases of reduced susceptibility to this antibiotic (vancomycin intermediately susceptible S. aureus, VISA) and heterogeneous VISA (hVISA) have been reported worldwide. The mechanism of vancomycin decreased susceptibility is poorly understood nowadays.  In this work we describe the characterization of two MRSA isolates recovered from a single patient suffering bone and joint infection: before and after vancomycin treatment (D1 and D2 respectively). Vancomycin and oxacillin susceptibility were determined according to CLSI recommendations. Vancomycin MICs were 0.5 and 1µg/ml (D1 and D2 respectively). In contrast, susceptibility to oxacillin decreased from 128µg/ml (D1) to 2µg/ml (D2). Methicillin and vancomycin resistance phenotypes were studied by population analysis. By PAP-AUC (area under the curve in the population analysis) both isolates were categorized as hVISA. Genotypic analysis revealed the presence of 550bp mecA fragment but SCCmec type could not be characterized by PCR mapping using conventional approaches. Both isolates showed identical PFGE patterns suggesting that the loss of oxacillin resistance is not due to SCCmec excision. An increased cell wall thickness was observed by transmission electron microscopy when D2 was compared with D1. D2 derived mutants were selected in increasing vancomycin concentrations. These mutants have vancomycin MIC of 8µg/ml and unexpectedly oxacillin MIC also increased (32µg/ml). Further studies are ongoing to determine the precise mechanism involved in this phenomenon