Naslov
Sequence heterogeneity in Giardia duodenalis genes and its relevance for genotyping studies

Autori
Cacci&ograve ; , Simone Mario ; Beck, Relja ; Lalle, Marco ; Marinculić, Albert ; Pozio, Edoardo

Vrsta, podvrsta i kategorija rada
Sažeci sa skupova, sažetak, ostalo

Skup
The Second International Giardia and Cryptosporidium Conference

Mjesto i datum
Morelia, Meksiko, 13.05.2007. - 18.05.2007

Vrsta sudjelovanja
Plenarno

Vrsta recenzije
Nije recenziran

Ključne riječi
Giardia dudenalis; heterogeneity; intra-assemblage variability

Sažetak
Giardia duodenalis is a widespread parasite of mammalian species, including humans. Due to its invariant morphology, investigation on aspects such as host specificity and transmission patterns requires direct genetic characterization of cysts from host samples. The aims of this study were: 1) to determine the intra-assemblage patterns of mutations ; 2) to define multilocus genotypes (MLGs) for assemblages A-F ; and 3) to compare MLGs of human and animal origin in order to estimate the occurrence of zoonotic transmission. A systematic analysis of G. duodenalis isolates from human (n=76) and animal (n=120) was performed by using PCR amplification and direct sequencing of 4 different genes. We found that, with the exception of the small subunit ribosomal RNA gene, the β -giardin (BG), glutamate dehydrogenase (gdh), and triose phosphate isomerase (tpi) genes display high levels of intra-assemblage variability, and define a large number of subtypes, which can be combined to identify MLGs for each assemblage. However, direct sequencing of PCR products also revealed high levels of sequence heterogeneity (the presence of 2 nucleotides at the same position, or mixed positions), a finding that was recently reported by other researchers. This phenomenon appears to be nonrandom with respect to G. duodenalis assemblages. Indeed, mixed positions were absent in all sequences from assemblage A isolates, and, therefore, MLGs can be defined unambiguously. Interestingly, comparison of assemblage A MLGs of human and animal origin showed little support for zoonotic transmission. In assemblage E, mixed positions were detected in all genes, but their number was small (2/11 in BG, 1/12 in tpi, and 3/9 in gdh). The number of isolates of assemblage F tested was too small to draw firm conclusions, albeit mixed positions were rarely observed. These results suggest that MLGs can be determined in the phylogenetically related assemblages A, E and F. On the contrary, in isolates from assemblage B, C and D, mixed positions were more frequently scored (for example, 10/26 in BG, 12/50 in tpi and 15/36 in gdh, among assemblage B isolates). Importantly, isolates that show mixed positions at one gene also show the same feature at the other genes (with some exceptions, however). This makes quite difficult the exact identification of MLGs in those assemblages, and has particularly important implications for genotyping studies of assemblage B isolates. The mechanisms potentially involved in this phenomenon (i.e., true mixed infections, allelic sequence heterogeneity, retention of ancestral polymorphisms and introgression) will be discussed.

Izvorni jezik
Engleski

Znanstvena područja
Biologija, Javno zdravstvo i zdravstvena zaštita, Veterinarska medicina

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