The Classic Paper of Tobie, Von brand, and Mehlman (1950) REVISITED

Abstract

In 1950, Tobie et al. described a diphasic blood agar medium that supported the cultivation of proventricular forms of the human sleeping sickness parasites, Trypanosoma brucei rhodesiense and T. b. gambiense, which was a major advance over similar systems used by other investigators. First, rabbit blood was used in place of human blood in preparation of the diphasic blood agar. Second, the culture system supported the differentiation of bloodstream-form trypanosomes, which could not at that time be cultured in vitro, into proventricular tsetse forms, which could be cultured. This provided the opportunity for controlled investigations of these parasites. Third, the trypanosomes grew to a high density, yielding about 2 X 107 organisms per milliliter, an adequate number for biochemical analysis of the cultured organisms. Tobie et al. (1950) exploited the system to carry out quantitative studies on sugar utilization by the parasites. They showed that the proventricular form of T. brucei was an aerobic fermenter, but that the sugar concentration in medium was not a limiting factor for their growth. This is now explained by knowledge of carbon source preference by these and other trypanosomes (Brun, 1982; Bienen et al., 1991; Ter Kuile, 1997; Obungu et al., 1999). When read today, the paper by Tobie et al. (1950) does not appear exciting or novel. However, one must remember that Tobie and colleagues worked in an era where little was known regarding trypanosome biochemistry and biology, and few systems were available for the investigation of biochemical processes in parasites. In fact, until the work of Hirumi et al. (1977), the only stage of the trypanosome that could be grown in vitro was the procyclic stage. The creative exploitation of the procyclic trypanosome culture system by Tobie et al. (1950) inspired other investigators to adapt similar systems as tools to investigate parasite biochemistry. The impact of the Tobie et al. (1950) paper on the field of parasite biochemistry is evidenced by frequent citation by their contemporaries, and an occasional citation even now. The paper has a well-deserved reputation as a classic.