Analysis of Variation in Tandem Repeats in the Intron of the Major Surface Glycoprotein Expression Site of the Human Form ofPneumocystis carinii

Variation in the tandem repeats in the expression site of the human-derived Pneumocystis carinii major surface glycoprotein gene was characterized by denaturing gel electrophoresis. The number of repeats in 147 isolates ranged from 2 to 6, with 2, 3, and 4 repeats being the most common. Sequence analysis identified 3 types of repeat units that differed by 1 nucleotide, which suggests a hierarchy of evolution of human-derived P. carinii. Examination of sequential samples obtained from 6 patients at an interval of 10-90 days showed an identical repeat pattern in each patient. However, in 2 of 4 patients with 2-3 different samples obtained within 4 days, different repeat patterns were observed among the samples. Quantifying the number of repeats by denaturing gel electrophoresis is a simple and rapid-typing method that can be used alone or in combination with other methods to study the epidemiology of P. carinii.