Efficient synchronization of Plasmodium knowlesi in vitro cultures using guanidine hydrochloride

BACKGROUND: Long-term in vitro culture of blood stage Plasmodium parasites invariably leads to asynchronous parasite development. The most often used technique to synchronize Plasmodium falciparum culture is sorbitol treatment, which differentially induces osmotic lysis of trophozoite- and schizont-infected red blood cells due to presence of the new permeation pathways in the membranes of these cells. However, sorbitol treatment does not work well when used to synchronize the culture-adapted Plasmodium knowlesi A1-H.1 line. METHODS: A number of common solutes were tested in lieu of sorbitol for synchronization of P. knowlesi A1-H.1 ring stage. RESULTS: Guanidine hydrochloride was found to selectively lyse trophozoite- and schizont-infected red blood cells, yielding highly synchronous and viable rings. CONCLUSIONS: A method for synchronization of P. knowlesi in human red blood cells was developed. Requiring only common laboratory reagents, this method is simple and should be applicable to most laboratory settings.