New automated method for determining postantifungal effect of amphotericin B against Candida species: effects of concentration, exposure time, and area under the curve

Abstract

The postantifungal effect (PAFE) of amphotericin B was determined with a BacT/Alert automated system, which is based on the colorimetric detection of CO(2). The levels of accuracy and precision of the automated method were high. Longer PAFEs were obtained for Candida albicans (P < 0.001), C. glabrata (P < 0.01), and C. krusei (P < 0.01) at increasing amphotericin B concentrations and exposure times.

FIG. 1.

(A) Relationship between log₁₀ CFU/ml of the starting inocula and time to positive growth signal in the control Pedi-BacT bottles. The upper line (○) represents a regression line where y = 7.36 − 0.24x (for inocula of sizes greater than 4.5 log₁₀ CFU/ml [n = 56]). The lower line (▿) represents a regression line where y = 8.15 − 0.30x (calculated from inocula of sizes <4.5 log₁₀ CFU/ml [n = 17]). The regression line representing inocula of larger sizes (broken line) has been extended to allow comparison with that representing those of smaller size (lower solid line). Some of the symbols represent multiple samples with identical values. (B) Growth curves of C. albicans ATCC 90028 with three different starting inoculum concentrations.

FIG. 2.

The relationships between AUCs of amphotericin B at various concentrations and PAFEs on C. albicans ATCC 90028 after exposure times of 30 (□) and 60 (▪) min.