Comparative evaluation of alternative methods for broth dilution susceptibility testing of fluconazole against Candida albicans

Abstract

A comparative evaluation of methods for broth macro-and microdilution susceptibility testing of fluconazole was conducted with 119 clinical isolates of Candida albicans. Macro-and microdilution testing were performed according to National Committee for Clinical Laboratory Standards recommendations. For reference macrodilution testing, an 80% inhibition endpoint (MIC 80%o) was determined after 48 h of incubation in accordance with National Committee for Clinical Laboratory Standards proposed standard M27-P. Microdilution endpoints were scored as the first tube or well in which a prominent reduction in turbidity (score 2 out of a possible 4) was observed compared with the growth control (Micro MIC-2). Alternative endpoint criteria were assessed independently of the reference MIC 80%o and Micro MIC-2 values and included a colorimetric microdilution endpoint determined by using an oxidation-reduction indicator (Alamar Blue; Alamar Biosciences Inc., Sacramento, Calif.). The MICs for the two microdilution test systems were read after 24 and 48 h of incubation. The percentage of fluconazole MICs within 2 doubling dilutions of the macrodilution reference values was 94% for both microdilution tests read at 24 h. Agreement was slightly lower at 48 h and ranged from 91 to 93%. Comparison of Micro MIC-2 and colorimetric microdilution MICs resulted in agreements of 97 and 93% at 24 and 48 h, respectively. These results show excellent agreement among alternative methods for fluconazole susceptibility testing.

Comparison study of broth macrodilution and microdilution antifungal susceptibility tests for the filamentous fungi

“…Recently, other studies comparing macro-and microdilution susceptibility testing methods in yeasts have been performed (1,8,9,14,16) which demonstrated a good agreement between both methods and revealed the utility of the microdilution method in susceptibility testing of pathogenic yeasts. The recent increase of emerging opportunistic filamentous fungi pathogenic to humans (3) also makes it necessary to have at one's disposal a reproducible standardized susceptibility test for these microorganisms which would lead to protocols for proper antimycotic treatment.…”

In Vitro Antifungal Susceptibility Testing

“…Macrodilution broth testing was established as the reference standard for antifungal susceptibility testing, serving as the basis for comparison with all alternative methods. [11][12][13][14][15][16][17][18][19][20] Detailed procedures for performing macrodilution and microdilution tests of Candida sp and C. neoformans are available elsewhere. 8 The methods were developed to facilitate conformity among laboratories and to be used as references for development of other methods.…”

“…Initially, M27-A recommended broth macrodilution methods, but simpler methods by broth microdilution were determined to be equally effective. [9][10][11] Other methods are available, although problems are encountered testing various organisms and antifungal agents.…”

In vitro antifungal resistance of oral Candida albicans strains in non‐AIDS Patients

“…However, even in immunocompetent patients some cases of oral candidosis are refractory to treatment or follow a pattern of initial success with subsequent relapse. This might be related to the development of resistant C. albicans strains, but susceptibility testing is not standardized and not routinely available (19), and information related to this problem is scarce in non-AIDS patients (14,17). The aim of this study was to evaluate the in vitro antifungal resistance of oral C. albicans strains from a cohort of supposedly HIV-negative patients with clinical symptoms of oral candidosis.…”