Abstract:

Objective To evaluate the performance of a three-gene typing system in the determination of Treponema pallidum （Tp） genotypes. Methods To determine the genotypes of Tp, three targets were assessed, including the number of 60 base-pair repeats, restriction fragment length polymorphism （RFLP） pattern of tprEGJ gene after MseI digestion and the sequence of tp0548 gene. The DNA extracted from the Nichols strain of Tp served as the positive control, and that from the moist ulcer of patients with genital herpes and negative RPR or TPPA test results served as the negative control. To validate the typing method, clinical specimens were collected from the moist skin lesions of patients with primary or secondary syphilis, and subjected to the amplification of polA gene by PCR. The enhanced molecular typing system was used to determine the genotypes of Tp in Tp DNA-positive specimens. Results The Nichols strain harbored a genotype of 14a/a. No amplification of any of the three target genes was found in the negative control. The arp gene, tprEGJ gene and tp0548 gene were amplified from 94.1%, 91.2% and 94.1% of the 40 clinical specimens, and the genotype was successfully determined by the three-gene typing system for 91.2% of the clinical Tp strains. The predominant type of arp, tprEGJ and tp0548 genes was 14 repeats, d and f, respectively in these clinical Tp isolates. Conclusion The enhanced molecular tying method for Tp exhibits high sensitivity, specificity and discrimination potential.

Key words: Clinical strains