LACK OF BACITRACIN INHIBITION BY GROUP A BETA-HEMOLYTIC STREPTOCOCCI

Abstract

Sixty-four cultures obtained from Costa Rican children with acute pharyngitis were evaluated for the presence of Group A beta-hemolytic streptococci (GABHS) by the bacitracin inhibition test performed on primary plates. Of the thirty-three cultures showing beta-hemolytic, only two (9%) demonstrated bacitracin inhibition. The Directogen latex agglutination test was performed on mixed colonies from the 33 plates demonstrating beta-hemolysis. Of these, 12 (36%) were positive for GABHS, 19 were negative and 2 were uninterpretable. Of the 12 positives, 8 (24%) could be isolated and confirmed as Group A by the Phadebact Streptococcal Grouping Method. Four (12%) could not be isolated. These data suggest that there is a high rate of bacitracin resistance among GABHS in Costa Rica, and that the bacitracin disc inhibition test on primary plates should not be relied upon due to a lack of sensitivity inherent in the technique.

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