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Journal of Clinical Microbiology, July 2007, p. 2162-2165, Vol. 45, No. 7
0095-1137/07/$08.00+0     doi:10.1128/JCM.00063-07
Copyright © 2007, American Society for Microbiology. All Rights Reserved.

Discrepancy in Antimicrobial Susceptibility Test Results Obtained for Oral Streptococci with the Etest and Agar Dilution{triangledown}

Eiman M. Mokaddas,1* Nathaneal O. Salako,2 Leeba Philip,2 and Vincent O. Rotimi1

Department of Microbiology, Faculty of Medicine,1 Department of Developmental and Preventive Science and Biochemical Sciences, Faculty of Dentistry, Kuwait University, Safat, Kuwait2

Received 9 January 2007/ Returned for modification 26 February 2007/ Accepted 17 April 2007

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.

* Corresponding author. Mailing address: Department of Microbiology, Faculty of Medicine, Kuwait University, P.O. Box 24923, Safat 13110, Kuwait. Phone: (965) 498 6512. Fax: (965) 533 2719. E-mail: e.mokaddas{at}hsc.edu.kw

{triangledown} Published ahead of print on 2 May 2007.

Journal of Clinical Microbiology, July 2007, p. 2162-2165, Vol. 45, No. 7
0095-1137/07/$08.00+0     doi:10.1128/JCM.00063-07
Copyright © 2007, American Society for Microbiology. All Rights Reserved.





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