Genotyping isolates and clones of Giardia duodenalis by polymerase chain reaction: implications for the detection of genetic variation among protozoan parasite species.

Detection of genetic variation among microorganisms can be done by DNA fingerprinting using the polymerase chain reaction (PCR). Application of primers directed to polymorphic DNA leads to the amplification of DNA fragments which differ in length when different species or isolates of a single species are compared. It has been demonstrated that PCR primers resembling eukaryotic repeat motifs enable the straightforward genetic differentiation of Giardia duodenalis isolates. Depending on the repeat motif, genetic variation between cloned G. duodenalis lines could also be detected. DNA polymorphisms could also be detected by random amplification of polymorphic DNA (RAPD) analyses. When the results obtained for G. duodenalis are compared to those found for another protozoan parasite, Naegleria fowleri, clear differences are encountered. In contrast to the findings for G. duodenalis, the repeat motif primers did not allow the discrimination of 'N. fowleri isolates. Apparently, as determined by this PCR-mediated genotyping, genetic variation occurs in G. duodenalis with increased frequency at the isolate level as compared to N. fowleri. The possible implications of this observation for clonality or the definition of a species in protozoan parasites will be discussed.