Flow cytometry, a useful tool for detecting the lethal effect of pentamidine on Leishmania viannia complex promastigote forms.

Flow cytometry (FC), combined with propidium iodide as supravital colorant, was used to study Leishmania(subgenus Viannia)panamensis [L (V) panamensis] complex strain susceptibility to meglumine antimoniate, sodium stibogluconate and pentamidine. Despite all drugs examined being leishmanicidal to axenic forms in in vitro trials (in the presence of macrophages), axenic amastigotes directly exposed to these drugs were highly resistant under our experimental conditions. A direct lethal effect on promastigotes, detectable by FC, was only obtained with pentamidine after in vitro treatment of both promastigotes and axenic amastigotes with the drugs. Pentamidine's rapid lethal effect, as detected by FC, could be further confirmed in short- and long-term parasite cultures after exposure to a drug. FC's suitability for measuring L (V) panamensis complex's promastigote susceptibility to pentamidine, shortly after in vitro drug exposure, might be useful in monitoring clinical trials with this drug and facilitating rapid pentamidine-resistant natural isolate identification.