Clonal diversity of the glutamate dehydrogenase gene in Giardia duodenalis from Thai Isolates: evidence of genetic exchange or Mixed Infections?

Background: The glutamate dehydrogenase gene (gdh) is one of the most popular and useful genetic markers for the genotypic analysis of Giardia duodenalis (syn. G. lamblia, G. intestinalis), the protozoan that widely causes enteric disease in humans. To determine the distribution of genotypes of G. duodenalis in Thai populations and to investigate the extent of sequence variation at this locus, 42 fecal samples were collected from 3 regions of Thailand i.e., Central, Northern, and Eastern regions. All specimens were analyzed using PCR-based genotyping and recombinant subcloning methods. Results: The results showed that the prevalence of assemblages A and B among these populations was approximately equal, 20 (47.6%) and 22 (52.4%), respectively. Sequence analysis revealed that the nucleotide diversity of assemblage B was significantly greater than that in assemblage A. Among all assemblage B positive specimens, the allelic sequence divergence within isolates was detected. Nine isolates showed mixed alleles, ranged from three to nine distinct alleles per isolate. Statistical analysis demonstrated the occurrence of genetic recombination within subassemblages BIII and BIV was likely. Conclusion: This study supports increasing evidence that G. duodenalis has the potential for genetic exchange

Determination of discriminatory power of genetic markers used for genotyping Giardia duodenalis

Small subunit ribosomal DNA (SSU-rDNA), glutamate dehydrogenase (gdh), beta-giardin, triosephosphate isomerase (tpi), and elongation factor 1-alpha (ef1-alpha) genes are useful genetic markers for genotypic analysis of the intestinal protozoan, Giardia duodenalis (syn. G. lamblia, G. intestinalis), the cause of enteric disease in humans. To quantitatively compare the discriminatory power of these loci, 43 fecal samples were collected from central, northern and eastern Thailand and G. duodenalis specimens were analyzed using PCR-based genotyping and subcloning methods. Approximately equal prevalence of assemblage A (21) and B (22) were present among these populations. Analysis of Simpson's index and Wallace coefficient values from assemblage B isolates together with the data obtained from Gen Bank showed that the combination of two loci provides a higher discrimination power for subgenotyping G. duodenalis than using any single locus