Direct application of Etest to gram-positive cocci from blood cultures: quick and reliable minimum inhibitory concentration data.

The Etest was applied directly to 100 Gram-positive bacterial strains from blood cultures to measure their minimum inhibitory concentration (MIC). Results showed 100% concordance of MIC data between a direct Etest method and the standard Etest method for Streptococcus pneumoniae, beta-hemolytic streptococci, and viridans group streptococci. In addition, direct Etest for Staphylococcus aureus, coagulase negative staphylococci, Enterococcus faecium, and Enterococcus faecalis showed 83 to 100% correlation with standard Etests. These data indicate that the Etest is useful to obtain MIC data on Gram-positive cocci (especially streptococci) directly from positive blood cultures. The advantages of a direct Etest are two fold: MIC results can be obtained 24 hours earlier than standard methods and a more representative population of the bacterial isolate is tested.