Adaptation of Leishmania to In Vitro Cultivation at 37 C*

Abstract

SYNOPSIS Promastigotes of Leishmania donovani 3S grown in Tobie's modified medium (Tm) at 25 C multiplied at 37 C after short periods of growth at 32 and 35 C. Only inocula from logarithmic phase cultures grew when placed at 32 C. Amastigotes placed at 32, 35, or 37 C became promastigotes but did not multiply upon transfer. The shortest period required for adaptation of 3S promastigotes to 37 C was 44 days (∽66 generations requiring 18 serial transfers). Addition of chick embryo extract to the medium was unnecessary for growth at elevated temperatures. Promastigotes of the Khartoum strain could not be acclimated to temperatures above 35 C.The long‐lasting nature of the adaptation was indicated by (a) ability of 37 C‐acclimated promastigotes to grow at this temperature after 14 serial transfers (∽100 generations) at 25 C, and (b) immediate growth of promastigotes at 37 C in cultures inoculated with homogenized hamster spleen previously infected with 37 C acclimated cells. The ability of the temperature‐adapted promastigotes to grow at 37 C was lost after 30 serial transfers (224 generations) at 25 C. Since sexual reproduction has not been demonstrated in Leishmania, it was impossible to ascertain whether acclimation was a consequence of mutation or represented a dauermodification.