Evaluation of molecular techniques to biotype Giardia duodenalis collectedduring an outbreak

Twenty-seven Giardia duodenalis cyst-positive specimens (human, animal, or drinking water) were obtained from a waterborne outbreak in a community in British Columbia, western Canada. Parasite isolates were characterized usin g molecular techniques at 4 different steps of organism retrieval. None of the drinking water samples (n = 20) infected gerbils and none was successfu lly amplified using polymerase chain reaction (PCR). We were able to genoty pe 4 of 7 (human and animal) isolates by amplification of DNA from original specimens at the triosephosphate isomerase (tpi) gene locus using PCR foll owed by restriction fragment length polymorphism (RFLP) analysis. Five of t he original specimens inoculated into Mongolian gerbils (Meriones unguicula tus) were infective and genotyped at the tpi locus using parasite material collected from the gerbil (cysts and trophozoites). Pulsed field gel electr ophoresis (PFGE) was used to biotype trophozoites collected from the gerbil s as well as trophozoites from the 4 isolates that adapted to culture. Four of these 5 isolates displayed the same (designated outbreak) biotype at al l parasite retrieval steps with all molecular techniques including the orig inally amplified isolates. PCR-RFLP identified an additional biotype group. The 4 isolates that adapted to in vitro culture were also characterized by isoenzyme electrophoresis (IE). Biotype groups identified in these axenize d isolates were all the same with each molecular technique (PCR-RFLP, PFGE, IE) tested. Results of this study demonstrate a need for more sensitive mo lecular methods to detect and characterize Giardia in original host and env ironmental samples. Results are also consistent with evidence of biotype ch anges that occur during the presently used process of isolate retrieval.