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) panamens is] complex strain susceptibility to meglumine antimoniate, sodium stiboglu conate and pentamidine. Despite all drugs examined being leishmanicidal to axenic forms in in vitro trials (in the presence of macrophages), axenic am astigotes directly exposed to these drugs were highly resistant under our e xperimental 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 l ethal effect, as detected by FC, could be further confirmed in short- and l ong-term parasite cultures after exposure to a drug. FC's suitability for m easuring L (V) panamensis complex's promastigote susceptibility to pentamid ine, shortly after in vitro drug exposure, might be useful in monitoring cl inical trials with this drug and facilitating rapid pentamidine-resistant n atural isolate identification. (C) 2001 Academic Press.