Antifungal susceptibility testing of Candida species by flow cytometry

The feasibility of flow cytometric antifungal susceptibility testing has be en studied using the fluorescent anionic membrane potential probe, bis-(1,3 -dibutylbarbituric acid) trimethine oxonol [DiBAC(4)(3)]. The in vitro anti fungal susceptibility testing of amphotericin B was performed on 8 Candida isolates from clinical specimens and 2 ATCC strains by flow cytometry with the results compared to those of the National Committee of Clinical Laborat ory Standards (NCCLS) M27-T, broth macrodilution method, The flow cytometri c method is based on an increase of fluorescence given out by DiBAC(4)(3) i n fungi when they are killed by antifungal agents. Minimum inhibitory conce ntration (MIC) of amphotericin B ranged from 0.25 to 1 mu g/mL. All results agreed within +/-2 dilution between the flow cytometric method and the M27 -T method. MIC with ATCC strains were within recommended ranges of M27-T, T he new flow cytometric method revealed a clear and distinct reproducible te st end point, A four hr of incubation was sufficient for the test. In concl usion, flow cytometry using DiBAC(4)(3) is a rapid acid accurate in vitro a ntifungal susceptibility testing method.