INTRODUCTION: Methicillin resistant Staphylococcus aureus (MRSA) infections are increasing, both in hospitals and the community. Vancomycin is the main antibiotic used to treat MRSA infections and this widespread use led to the emergence of isolates with reduced susceptibility. Since 2009 it was established that the susceptibility test to vancomycin should be determined using minimum inhibitory concentration (MIC). OBJECTIVE: Based on the above, this study aimed to determine vancomycin susceptibility in MRSA isolates comparing antimicrobial susceptibility methods recommended by Clinical and Laboratory Standards Institute (CLSI). METHODOLOGY: We analyzed 46 isolates of S. aureus resistant to methicillin from Mãe de Deus Hospital, in Porto Alegre, Brazil. MICs for S. aureus isolates were determined using Etest® strips and were correlated with broth macrodilution method, Etest® and MicroScan Walk Away 96 (Siemens®). RESULTS: All strains were susceptible to vancomycin by all methods, however, the Etest® strips showed higher MIC values compared with broth macrodilution. MicroScan Walk Away 96 (Siemens®) shows similar results compared with other methods for presenting the value of sensitive as < 2 µg/ml. DISCUSSION AND CONCLUSION: The Etest® method overestimates the MIC values, however it is easily and quickly accomplished. In the other hand, broth macrodilution is very laborious and time consuming. MicroScan Walk Away 96 (Siemens®) results are accurate, but does not provide the exact MIC value requiring an additional test to estimate the effectiveness of treatment. In conclusion, the Etest® can be used as an alternative for routine monitoring.
Microbial sensitivity tests; Methicillin-resistant Staphylococcus aureus; Vancomycin
