Antifungal susceptibility of Candida clinical isolates in Canada: a ten-year review

Abstract number: 1733_1455

Fuller J., Sand C., Rennie R.

Objective: The Canadian National Centre for Mycology (NCM) provides susceptibility testing of yeast and filamentous fungi for Canadian laboratories submitting specimens for routine mycology or isolates for confirmatory testing. The purpose of this study was to determine the antifungal susceptibility rates of clinical Candida isolates submitted to the NCM over the past ten years.

Methods: Susceptibility testing of Candida isolates was performed according to the Clinical Laboratories Standards Institute (CLSI) M27A-2 document for broth microdilution (BMD) testing of yeast. BMD panels containing RPMI broth with MOPS buffer, and doubling dilutions of antifungal agents, were inoculated with 10e3 CFU/mL of the test isolate and incubated at 35 degrees C for 48 hours. Antifungal agents included amphotericin B, 5-fluorocytosine, fluconazole, intraconazole, voriconazole, and caspofungin; the latter two agents were tested against 2004 and 2005 isolates only. The 90% minimum inhibitory concentration (MIC₉₀) averaged from total annual isolates was recorded to monitor temporal trends.

Results: From 1995 to 2005 the most common species submitted to the NCM annually included C. albicans, C. glabrata, C. parapsolosis, and C. tropicalis with 801, 421, 188, and 96 total isolates, respectively, and primarily consisted of invasive isolates. Overall, MIC₉₀ values remained unchanged and showed little evidence of reduced susceptibility to the antifungal agents tested; amphotericin B ≤ 4 mg/L, 5-fluorocytosine ≤ 8 mg/L, intraconazole ≤16 mg/L, voriconazole ≤ 2 mg/L, and caspofungin ≤ 2 mg/L. However, for fluconazole the C. albicans MIC₉₀ decreased from 16 mg/L to 4 mg/L while C. glabrata MIC₉₀ increased from 8 mg/L to 64 mg/L.

Conclusion: Despite reported increases of invasive candidiasis, this passive surveillance of Candida susceptibility rates indicates that recommended antifungal agents remain quite active against the most common infecting species. However, C. glabrata resistance to the azoles is increasing in Canada. As new antifungal agents become available, continued and increased surveillance is necessary to monitor the emergence of resistance.