Avaliação comparativa do Phoenix®, VITEK® 2, Etest® e Teste de Microdiluição em Caldo, para determinação do perfil de sensibilidade à vancomicina em Staphylococcus aureus isolado de infecção da corrente sanguínea

Abstract

Staphylococcus aureus bacteremia causes significant morbidity and mortality, mainly by methicillin-resistant S. aureus (MRSA). Currently, vancomycin is the main choice for treatment of MRSA infections. Broth microdilution (BMD) remains the gold standard test for measuring vancomycin minimum inhibitory concentration (MIC). However, most clinical laboratories uses practical methods in the routines, but these methods may not determine vancomycin MIC values accurately. The aim of this study was to evaluate the accuracy of VITEK®2, Phoenix®, Etest® methods to determinate MIC values against BMD. A total of 78 strains (27 methicillin-sensitive S. aureus and 51 MRSA) were isolated from bloodstream infections on patients admitted to an Universitary Hospital in Rio de Janeiro city, Brazil. The vancomycin MIC was determined following Clinical and Laboratory Standards Institute (CLSI) and the manufacturers' recommendations. Also was performed SCCmec typing, in order to identify a possible correlation between the types found with vancomycin MIC values verified in this analysis. Most of all isolates showed values of MIC = 1 μg/mL by BMD and Phoenix®, while Etest® and VITEK® 2 determined the majority with MIC = 1.5 and 0.5 μg/mL, respectively. Thus, Etest® and VITEK® 2 tended to overestimate and underestimate, respectively, the MIC values. Three MRSA isolates that were vancomycin susceptible by BMD were considerated vancomycin-intermediate by Etest®. The SCCmec II (39%) and IV (51%) types were the most frequent, and there was no correlation between the type of SCCmec and the MIC values. The results showed that vancomycin MICs vary according to the test method. It is essential that attending physicians consider the differences in MIC results determined by different methods, since the MIC value is generally one of the laboratorial parameters used to select the appropriate therapy.