Differentiation and limited proliferation of isolated Leishmania mexicana amastigotes at 27 degrees C.

We have demonstrated here that while many amastigotes of both Leishmania mexicana amazonensis and Leishmania mexicana mexicana differentiate to promastigotes when placed in culture at 27 degrees C, many others remain as amastigotes in their proliferative cycle. We have used this system to examine the effects of the anti-leishmanial compounds amphotericin B, 4-pentenoate and sodium stibogluconate (Pentostam) on the proliferation and differentiation of isolated extracellular amastigotes. Amphotericin B and 4-pentenoate showed little preferential effect on amastigote proliferation over promastigote proliferation although Leishmania mexicana mexicana (strain M379) was generally more resistant to these compounds than Leishmania mexicana amazonensis (strain LV78). This relative resistance was also observed in axenic cultures of proliferating promastigotes. L.m. mexicana amastigote differentiation was inhibited by amphotericin B and 4-pentenoate. Pentostam displayed a greater effect on amastigote differentiation than proliferation in both sub-species although again, a higher concentration was required to produce the same effect in L.m. mexicana.