Limitations of tpi and bg genes sub-genotyping for characterization of human Giardia duodenalis isolates

The intestinal protozoan Giardia duodenalis includes 2 genetically distinct assemblages, A and B, which are responsible for human infections. Little is known so far on the genotypes of G. duodenalis human isolates in France. The present characterization of 19 French clinical isolates was aimed at determining their genotype patterns and associations with clinical symptoms, and in vivo metronidazole resistance, respectively. Based on both triose-phosphate isomerase (tpi) and β-giardin (bg) gene sequences, twelve isolates were identified as assemblage A, and 7 as assemblage B for the 2 gene loci. Sub-genotyping heterogeneities were observed in 15/19 isolates attributed to either A or B assemblage. They include frequent mismatches and intra-assemblage discordances and mixed positions, which were found more frequently in tpi than in bg sequences, and in assemblage B than in assemblage A sequences. No association was found between sub-genotypes, clinical symptoms and metronidazole sensitivity. Present data underline the need for improvements in the standardization of G. duodenalis multilocus genotyping approach for further molecular epidemiologic studies of giardiasis.

Research highlights
► Genotypic characterization by sequencing of bg and tpi genes determine the Giardia duodenalis assemblage.
► Sequencing of these genes does not always determine the sub-assemblage.
► Multilocus genotyping methodologies must be improved and harmonized.