III - TYPING METHODS TO APPROACH PNEUMOCYSTIS-CARINII GENETIC-HETEROGENEITY

The study of the genetic heterogeneity of P. carinii is complicated by the lack of an in vitro culture system, as well as by the likely occu rrence of co-infections with several special forms or types in a singl e host. Karyotyping and multilocus enzyme electrophoresis are useful f or studies at the evolutionary level. However, these methods require a large number of cells, which prevents their use for the special form infecting humans. DNA sequence analysis of genomic regions is useful t o study P. carinii diversity, both at the evolutionary and epidemiolog ical levels. To type the special form specific to humans, several meth ods are currently used to detect polymorphism in PCR products of polym orphic regions of the genome: DNA sequencing, type-specific hybridisat ions, and single-strand conformation polymorphism. All these methods s till need evaluation. The frequency of potential co-infections in huma ns determined by these various methods is different. The differences c ould be due to methodological problems or to real variations between p atient populations, geographical locations and/or prophylaxis regimens . In the future, elucidating the population structure of P. carinii an d the frequency of potential co-infections is going to be crucial for a better understanding of its epidemiology, and thus for a better prev ention of P. carinii pneumonia in humans. (C) 1998 Federation of Europ ean Microbiological Societies. Published by Elsevier Science B.V. All rights reserved.