Flow cytometric assessment of amphotericin B susceptibility in Leishmania infantum isolates from patients with visceral leishmaniasis

Amphotericin B susceptibility was measured by a flow cytometric membrane po tential assay in Leishmania infantum promastigotes isolated from 11 immunoc ompetent children treated with liposomal amphotericin B and 19 HIV-infected young adults treated with intralipid amphotericin B. Susceptibility levels were measured by the 90% inhibitory concentrations (IC90) representing the concentrations of drug that induced a 90% decrease in membrane potential c ompared with the control culture. In immunocompetent children, treatment wa s fully effective whatever the susceptibility of isolates to amphotericin B . In immunocompromised adults, on the contrary, unresponsiveness and relaps es could be observed in all cases and IC90 increased in the course of succe ssive treatments: a decrease of amphotericin B susceptibility in both proma stigote and amastigote forms could be observed in a patient who had six rel apses. These results suggest that the success of amphotericin B treatment d epends greatly on patient immunity status, and indicate that successive rel apses could enhance emergence of amphotericin B resistant isolates. The res ults demonstrate that the flow cytometric membrane potential assay can be u sed as an easy and reliable tool for studying the evolution of interactions between amphotericin B and the parasite membrane during long-term treatmen ts.