FLUCONAZOLE RESISTANCE IN CANDIDA SPECIES
Fluconazole is the most commonly used drug to treat candidiasis. Treatment failure may be associated with either some Candida species inherently resistant or due to acquired resistance to the drug.
Candida albicans, C. tropicalis, C. parapsilosis are common candida species assumed to be susceptible to fluconazole. Candida krusei is known to be intrinsically resistant to fluconazole but shows very little cross-resistance to higher triazoles like voriconazole. On the other hand, C. glabrata exhibits acquired resistance that spans all triazoles. Other less common candida species which can show reduced susceptibility to fluconazole are C.guillermondii,C. rugosa, C. inconspicua, and C. norvegensis.
Triazole susceptibilities to invasive candida species can be determined by recording minimal inhibitory concentration (MICs) using broth microdilution (BMD), e-test strips or zone diameters with triazole discs. The medium used for MIC testing is RPMI broth for BMD and RPMI agar for e-test strips; the cut-off point being the dilution showing more than 50% drop in growth rather than complete inhibition. For disc diffusion, the medium is Mueller-Hinton agar with 2% glucose and 0.5mcg/ml methylene-blue and a 25 mcg disc. The interpretative categories for fluconazole are susceptible (S), isolates whose MICs (≤ 8 mcg/ml, zone diameter ≥19 mm) are such that the infection may be appropriately treated with dose recommended for that agent;