Molecular Subtyping and Surveillance of Resistance Genes In Treponema pallidum DNA From Patients With Secondary and Latent Syphilis in Hunan, China.

Background: Over the past decade, the incidence of syphilis and widespread macrolide resistance in its etiological agent, Treponema pallidum subsp. pallidum, have become a major health concern across countries, including China. Regional trends in subtypes and antibiotic resistance can be monitored effectively by molecular surveillance programs. In this study, whole blood samples were used to assess circulating T. pallidum strains collected from various regions of Hunan, China, between 2013 and 2015.

Methods: Traditional polymerase chain reaction, targeting polA, tpp47, bmp, and tp0319 genes, was used as preliminary screening assay. About 455 polymerase chain reaction-positive specimens were obtained from 2253 whole blood samples of patients with secondary or latent syphilis. Molecular subtyping was performed using a Centers for Disease Control and Prevention-based typing method combined with an analysis of the variable region of tp0548 gene. Resistance to macrolides was analyzed by examining point mutations in 23S rRNA, and the presence of the G1058C point mutation within 16S rRNA associated with decreased susceptibility to doxycycline was assessed.

Results: Circulating T. pallidum strains were resolved into 32 subtypes, among which subtype 14d/f was predominant. A2059G mutation in 23S rRNA, and the G1058C mutation in 16S rRNA was absent, but the prevalence of A2058G mutation in 23S rRNA was 97.5%.

Conclusions: We found that it is possible to use whole blood to evaluate molecular subtypes and monitor antibiotic resistance in circulating T. pallidum strains, especially when chancres are absent. High frequency of macrolide-resistant T. pallidum indicates that macrolide antibiotics, such as azithromycin, should be avoided as a treatment option for syphilis in Hunan, China.