Evaluation of the E Test: A new quantitative antimicrobial susceptibility test. 2. Application for Streptococcus pneumoniae and Haemophilus influenzae strains

The E Test was applied to the MIC determination of different antimicrobial drugs for Streptococcus pneumoniae and Haemophilus influenzae strains isolated from pediatric infections. The E Test MICs were compared with those determined by the agar dilution method. The MIC values obtained by both methods were in agreement, regardless of the penicillin-susceptibility of the test strains or their β-lactamase producibility. However, the E Test MICs of imipenem, azithromycin and vancomycin for penicillin-insensitive strains of S. pneumoniae were one dilution higher than those determined by the agar dilution method. The E Test MICs were not affected by the addition of blood components. The E Test appears to be a reliable method for the determination of fastidious bacteria such as S. pneumoniae and H. influenzae.