INTERPRETATION OF TRAILING END-POINTS IN ANTIFUNGAL SUSCEPTIBILITY TESTING BY THE NATIONAL COMMITTEE FOR CLINICAL LABORATORY STANDARDS METHOD

Trailing endpoints remain a problem in antifungal susceptibility testi ng using the National Committee for Clinical Laboratory Standards (NCC LS) method, For isolates for which trailing endpoints are found, MICs of less than or equal to 1 mu g/ml at 24 h and of >64 mu g/ml at 48 h are usually observed. In a study of human immunodeficiency virus (HIV) -infected patients with oropharyngeal candidiasis, we identified three patients with multiple serial isolates for which trailing endpoints w ere observed,vith fluconazole. At 24 h, MICs were generally less than or equal to 1 mu g/ml by both broth macro-and microdilution methods, H owever, at 48 h, MICs were >64 mu g/ml, while the organism remained Su sceptible by agar dilution testing with fluconazole, Most episodes of oropharyngeal candidiasis with trailing-endpoint isolates responded to doses of fluconazole as low as 100 mg/day. Two patients had both susc eptible and trailing-endpoint isolates by NCCLS broth macro-and microd ilution testing; these isolates were found to be the same strain by pu lsed-field gel electrophoresis using restriction fragment length polym orphisms, Another patient had two different strains, one for which tra iling endpoints were observed and one which was susceptible at 48 h, T railing endpoints may be seen,vith selected isolates of a strain or ma y be a characteristic finding for most or all isolates of a strain, In addition, with isolates for which trailing endpoints are observed, re ading the endpoint for the NCCLS method at 24 h may be more appropriat e.