Abstract: Abstract: 【Objective】The objective of the present study was to examine sequence variation in the repetitive 529 bp DNA fragment among 9 T. gondii strains from different hosts and geographical locations in China, and to compare the sequences with that of the RH reference strain. 【Method】 The 529 bp fragment was amplified by PCR from genomic DNA of the 10 T. gondii strains, and the amplicons were purified, cloned into pGEM-T Easy vector and the recombinant plasmids were identified by colony PCR and digestion with endonuclease EcoR I, and then sequenced. 【Results】 Sequence variation in the repetitive 529 bp DNA fragment ranged between 0.8-2.9% among the 10 T. gondii strains, with sequence positions of 32-55 nucleotides being the most variable region. But the sequence variation was not related to virulence. 【Conclusion】The findings of the present study showed that the intraspecific variation in the repetitive DNA fragment was low and this repetitive DNA fragment provides an ideal genetic marker for the differentiation of T. gondii from other organisms, but it is not suitable for the studies of genetic variability within T. gondii.

Key words: Toxoplasma gondii, PCR, Repetitive 529 bp fragment, Sequence analyses, Genetic variation