Differentiation of Cryptococcus neoformans serotypes by isoenzyme electrophoresis

Cryptococcus neoformans has been divided into four serotypes by specific agglutination in immune rabbit sera. Based on mating characteristics of the perfect state and epidemiologic and biochemical differences, the serotypes have been divided into two major pairs. In an attempt to characterize the serotypes further, the authors studied 22 strains of C. neoformans by the technic of horizontal starch-gel isoenzyme electrophoresis. The glucose-phosphate isomerase and phosphoglucomutase of serotypes A, C, D, and a subset of the serotype B strains migrated to distinguishable locations in this system. The activities of the remainder of the serotype B strains co-migrated with the serotype C strains. Thus, this technic distinguishes all the serotypes of C. neoformans except for a subset of serotype B and should be a useful adjunct for further elucidation of the epidemiologic and biochemical differences among serotypes.