RESUMO
Extracting genomic DNA of pathogenic agents from formalin-fixed specimens is inherently difficult. Storage of samples in formalin results in nucleic acid cross-linking and DNA fragmentation. In this study, DNA was extracted from 45 Giardia-positive stool samples stored in formalin and subjected to PCR amplification targeting the triose phosphate isomerase (tpi), beta gardin (bg) and glutamate dehydrogenase (gdh) genes. Samples were rehydrated by using a descending alcohol series before DNA extraction using a commercial kit. This was followed by EDTA-mediated inhibition of DNase activity and prolonged treatment with proteinase K to digest contaminating proteins. DNA was amplified at rates of 64.4% (29/45) at the tpi, 40% (18/45) at the bg and 20% (9/45) at the gdh loci as seen on nested PCR. DNA quality was subsequently tested in a genotyping experiment which produced high-quality sequences at the tpi (41.2%; 12/29) bg (50%; 9/18), and gdh (22.2%; 2/9) loci and enabled differentiation of Giardia strains at the subtype level. The modified extraction protocol was effective at removing inhibitors and reversing cross-linking of DNA. However, PCR amplification was limited to short fragments of DNA which resulted in highest success rate on amplification of the shortest (334 bp) gene fragment tested.
Assuntos
DNA de Protozoário/isolamento & purificação , Fezes/parasitologia , Fixadores/efeitos adversos , Formaldeído/efeitos adversos , Giardia/genética , Sequência de Bases , Proteínas do Citoesqueleto/genética , DNA de Protozoário/química , DNA de Protozoário/genética , DNA de Protozoário/normas , Etanol/administração & dosagem , Genótipo , Técnicas de Genotipagem , Giardia/química , Giardia/classificação , Giardia/enzimologia , Glutamato Desidrogenase/genética , Humanos , Reação em Cadeia da Polimerase , Proteínas de Protozoários/genética , Solventes/administração & dosagem , Fatores de Tempo , Triose-Fosfato Isomerase/genéticaRESUMO
Giardia spp. are the causative agents of intestinal infections in a wide variety of mammals including humans and companion animals. Dogs may be reservoirs of zoonotic Giardia spp.; however, the potential for transmission between dogs and humans in Jamaica has not been studied. Conventional PCR was used to screen 285 human and 225 dog stool samples for Giardia targeting the SSU rDNA gene followed by multilocus sequencing of the triosephosphate isomerase (tpi), glutamate dehydrogenase (gdh), and ß-giardin (bg) genes. Prevalence of human infections based on PCR was 6.7 % (19/285) and canine infections 19.6 % (44/225). Nested PCR conducted on all 63 positive samples revealed the exclusive presence of assemblage A in both humans and dogs. Sub-assemblage A-II was responsible for 79.0 % (15/19) and 70.5 % (31/44) of the infections in humans and dogs, respectively, while sub-assemblage A-I was identified at a rate of 15.8 % (3/19) and 29.5 % (13/44) in humans and dogs, respectively. The predominance of a single circulating assemblage among both humans and dogs in Jamaica suggests possible zoonotic transmission of Giardia infections.