Trypanosoma b. brucei: a culture medium reverting a monomorphic to a pleomorphic strain

A monomorphic strain of Trypanosoma b. brucei cultured for 5 days at 37 degrees C in Eagle's Minimum Essential Medium (with or without feeder cells) supplemented with Nu-Serum became pleomorphic after inoculation into mice. Dividing stumpy forms were still seen in blood after the third mouse passage. The strain remained monomorphic when cultured in the medium supplemented with foetal calf serum. This supports the hypothesis that some slender forms, under certain conditions, have the genetic capability of transforming into stumpy forms which can multiply by binary fission in the mammalian host.