Abstract: Toxoplasma gondii is a parasitic protozoan infecting a variety of hosts with a worldwide distribution. The objective of the present project is to study the genotypes of T. gondii strains from different hosts and geographical locations in China employing the technique of PCR-linked restriction fragment length polymorphism (PCR-RFLP) utilizing the dense granule antigen GRA6 gene as genetic markers. Partial GRA6 sequence was amplified from strains ZS (human), SH (human), CN (pig), QH (sheep) and RH of T. gondii, the amplicons were digested with restriction enzyme Mse I, and then the digestion fragments were separated by agarose gel electrophoresis. Two different restriction profiles were observed among the five strains, with strains RH, SH and CN having identical banding patterns, whereas strains QH and ZS having a different banding pattern. Sequence analyses revealed that strains RH, SH and CN had almost identical GRA6 sequences and the same locations for two Mse I restriction sites, whereas strains QH and ZS had another type, almost identical sequences and the same locations for two Mse I restriction sites, consistent with results of PCR-RFLP analysis. Based on the results of PCR-RFLP and sequence comparison, strains RH, SH and CN were considered to represent genotype I of T. gondii, whereas strains QH and ZS represent genotype II of T. gondii, consistent with their virulence in mice. The results indicated that at least two different genotypes of T. gondii were present in China. These findings should have important implications for studying the molecular epidemiology, molecular ecology and population genetic structures of T. gondii strains from different hosts and geographic locations in China and elsewhere.

Key words: Toxoplasma gondii, GRA6, PCR-linked restriction fragment length polymorphism (PCR-RFLP), Sequence analysis