Antifungal drug susceptibilities of commensal Candida isolates

Two hundred and forty-two oral commensal yeast isolates were obtained from a convenience sample of 134 healthy 7- and 8-year-old children (65 males and 69 females). The isolates were initially tested for their susceptibilities to the antifungal azole drug fluconazole, using an agar diffusion method (Etest), which was suitable for screening large numbers of yeast isolates, and confirmed as equivalent to the broth microdilution reference method. Eighteen isolates from 7 children were found to have low fluconazole susceptibility according to guidelines published by the United States National Committee for Clinical Laboratory Standards (NCCLS). The isolates with low susceptibility were identified as either Candida tropicalis (n = 9 of 34 strains tested) or Candida glabrata (n = 9 of 13 strains tested). Selected isolates (6 susceptible and 7 with lower susceptibility to fluconazole) were also tested by a reference broth microdilution method for susceptibility to fluconazole and to a related over-the-counter azole antifungal, miconazole. A positive correlation between susceptibility to fluconazole and to miconazole was observed. The high rate (38 percent) of reduced susceptibility in commensal C tropicalis and C glabrata strains may represent a future treatment problem if the use of over-the-counter azole drugs increase.