DIFFERENTIATION OF MAJOR GENOTYPES OF GIARDIA-INTESTINALIS BY POLYMERASE CHAIN-REACTION ANALYSIS OF A GENE ENCODING A TROPHOZOITE SURFACE-ANTIGEN

The polymerase chain reaction (PCR) has been used to amplify in vitro a semi-conserved region of a gene encoding an M(r) 68-72000 surface an tigen of Giardia intestinalis trophozoites. Using primers specific for conserved nucleotide sequences identified within the promoter-distal portion of two homologous genes (tsp11 and tsa417) cloned previously f rom the G. intestinalis isolates Ad-1 (from Australia) and WB (from Af ghanistan), a single PCR-amplified DNA fragment of the expected size ( 0.52 kilobases) was obtained in high yield from either purified DNA or whole trophozoites of the Ad-1 isolate and from every 1 of 9 other ax enic G. intestinalis isolates belonging to genetic groups I and II (de fined previously on the basis of allozyme electrophoresis data-Andrews et al. 1989). Discernible product was recovered from as few as 2-4 tr ophozoites. In contrast, 6 G. intestinalis isolates that were assigned by allozymic analysis to genetic groups III/IV yielded small amounts of a 0-37-kilobase (kb) amplification product (with evidence in some s amples of an additional 0.4 or 0.18 kb fragment) but no 0.52 kb produc t. Two animal-derived isolates of G. duodenalis (one from an Australia n native rodent, Notomys alexis, the other from a domestic cat) also y ielded a single 0.37 kb PCR-amplified fragment, whereas an isolate fro m another cat produced a 0.34 kb fragment. No product was recovered fr om G. muris, a morphologically distinct species of Giardia. The result s demonstrate that different genotypes of G. duodenalis can be disting uished using this assay and that it is diagnostic for isolates belongi ng to two major clusters (groups I/II and III/IV) of G. intestinalis. The amplified DNA segment appears to be relatively conserved among gro up I and group II isolates of G. intestinalis. A related but clearly d istinct sequence seems to be conserved among group III/IV isolates of G. intestinalis and some isolates of G. duodenalis.