Discrepancies between results by E-test and standard microbroth dilution testing of Streptococcus pneumoniae for susceptibility to vancomycin.

Vancomycin susceptibility testing of Streptococcus pneumoniae by the E-test consistently resulted in MICs that were at the upper limit of the 1-microgram/ml susceptible category defined by current National Committee for Clinical Laboratory Standards guidelines and were always higher than MICs obtained by microbroth dilution. Three of five E-test results for S. pneumoniae ATCC 49619 were higher than the acceptable limits.