Pulsed-field gel electrophoresis as a method of biotyping of Giardia duodenalis

Abstract

Pulsed-field gel electrophoresis (PFGE) has allowed karyotypic characterization of protozoa at a species and a subspecies level. Different methods of PFGE have been applied to analysis of Giardia isolates from the major morphologic groups and of isolates from the G. duodenalis group. We developed a four-day method of contour-clamped homogeneous electric field PFGE that produced reliable chromosomal band separation for isolates from the G. duodenalis group. When a significant waterborne outbreak of giardiasis occurred in a town in British Columbia, this biotyping method was assessed by characterization of isolates associated with the outbreak. Results were compared with karyotypes obtained from isolates retrieved in other parts of the province, as well as with reference isolates. Isolates in this study were found to have 4-6 chromosomal bands estimated to be between 1 and 4 Mb in size. The chromosomal complement of the outbreak-associated isolates was relatively homogeneous and distinguishable from the non-outbreak-associated British Columbia and reference isolates. The present study showed this PFGE method to be useful in biotyping isolates of G. duodenalis. This study also exemplifies the degree of heterogeneity displayed at the genotypic level of Giardia, as well as the apparent stability of the outbreak-associated karyotype during transmission from original infecting animal through a water vehicle to human cases.