Discrepancy in antimicrobial susceptibility test results obtained for oral streptococci with the Etest and agar dilution.
A total of 270 viridans group streptococci (VS) isolated from healthy children, identified to the species level, were tested for their susceptibilities to penicillin, imipenem, erythromycin, and vancomycin. A total of 270 isolates and 1,080 organism-antibiotic combinations were evaluated. The overall susceptibility rates of all isolates obtained by the Etest (ET) versus agar dilution (AD) were 60.4% versus 61.8% for penicillin, 63.8% versus 63.9% for erythromycin, 90.6% versus 96% for vancomycin, and 99.1% versus 96.0% for imipenem, respectively. Major discrepancies occurred in the testing of the susceptibility of Streptococcus mutans to vancomycin, with 59.5% (ET) versus 100% (AD), followed by S. salivarius, with 84.1% versus 100%; S. oralis, with 82.1% versus 96.4%; and S. mitis, with 90% versus 100%, respectively. There were also differences in the rates of susceptibility of S. mutans, 66.5% (ET) versus 85.1% (AD), and S. intermedius, 82.9% versus 72.1%, respectively, to penicillin. General agreement between the results of ET and AD was obtained for 973 organism-antibiotic combinations out of 1,080 antibiotic combinations, i.e., 90.1%. Very major errors were found for 6.8% of isolates, and major errors were found for 3.2% of isolates; the minor errors were negligible. Agreement between the results of the two methods was 98.7% for penicillin, 94.6% for vancomycin, 96.9% for imipenem, and 99.9% for erythromycin. The highest rate of very major errors was for vancomycin, at 5.4%. The ET appears to be as efficient as AD for susceptibility testing of VS, except for vancomycin, where very major errors in the results were relatively high.
Mokaddas
Eiman M
EM
Department of Microbiology, Faculty of Medicine, Kuwait University, P.O. Box 24923, Safat 13110, Kuwait. e.mokaddas@hsc.edu.kw
Salako
Nathaneal O
NO
Philip
Leeba
L
Rotimi
Vincent O
VO
D000900:Anti-Bacterial Agents / Q000494:pharmacology*; D002648:Child; D015169:Colony Count, Microbial; D024901:Drug Resistance, Multiple, Bacterial; D006801:Humans; D008826:Microbial Sensitivity Tests; D009055:Mouth / Q000382:microbiology; D012107:Research Design; D013291:Streptococcus / Q000187:drug effects*
D000900:Anti-Bacterial Agents