Survey of amphotericin B susceptibility of Candida clinical isolates determined by Etest

Background and Purpose: The minimal inhibitory concentrations (MICs) of amphotericin B (AmB) determined by the National Committee for Clinical Laboratory Standards (NCCLS; NCCLS document M27-A) broth dilution method are in a relatively narrow ranges and this may lead to underestimation of the AmB-resistant rate in clinical isolates. We evaluated in vitro susceptibility of clinical isolates of Candida spp. to AmB using Etest and determined the distribution of AmB MICs in different species. Methods: We used the Etest (AB Biodisk, Solna, Sweden) to evaluate the MICs of Candida isolates randomly collected during 2001-2003 in a teaching hospital. Results: Of the 572 isolates evaluated, Candida albicans (50.7%) was the most common species, followed by Candida tropicalis (23.9%), Candida parapsilosis (13.1%), Candida glabrata (9.4%), Candida krusei (1.9%), and Candida guilliermondii (0.9%). The majority of isolates were from blood (85%). The minimal concentrations of AmB required to inhibit 50%/90% of the isolates (MIC50.MIC90) were 0.19/0.38 μg/mL for C. krusei, 0.125/0.38 μg/mL for C. glabrata, 0.094/0.25 μg/mL for C. tropicalis, 0.032/0.19 μg/mL for C. albicans, 0.016/0.125 μg/mL for C. parapsilosis, and 0.023/0.032 μg/mL for C. guilliermondii. Only 1 blood isolate of C. glabrata was resistant to AmB (MIC ?1 μg/mL) [0.17%]. 18.2% of isolates were less susceptible to AmB (MIC ?0.19 μg/mL) with the highest rates for C. krusei (63.6%), followed by C. glabrata (37.0%), C. tropicalis (29.9%), C. albicans (11.0%), C. parapsilosis (5.3%), and C. guilliermondii (0%). More isolates collected from patients with hematologic malignancy were less susceptible to AmB than those collected from those with other diseases (30.5% vs 15.4%, p<0.05). Conclusion: This study demonstrated that AmB resistance remains rare at this hospital in Candida clinical isolates despite increasing use of this agent during the past 4 decades. ? 2006 Journal of Microbiology, Immunology and Infection.