Macrolide resistance and molecular types of Treponema pallidum causing primary syphilis in Shanghai, China

The resurgence of syphilis in China requires laboratories to update their methods for molecular epidemiology investigation and surveillance. This study focuses on implementing polymerase chain reaction (PCR) diagnostic tests for syphilis and for detection of molecular subtypes and macrolide resistance among strains causing primary syphilis in the city of Shanghai, China.

Swabs were obtained from the genital lesions of 39 patients who presented with symptoms compatible with primary syphilis. Eight of the patients also provided whole blood samples. Swabs were also obtained from 10 patients without syphilis who presented with genital ulcers. PCR tests to amplify 3 common but unlinked treponemal genes were performed on DNA samples extracted from these specimens. Molecular subtyping was based on genetic characterization of 2 treponemal repeat genes, arp and tpr. Detection of macrolide resistance was accomplished by identification of the 23S ribosomal RNA gene mutation associated with the resistance pattern.

Thirty-eight patients with primary syphilis were found to have Treponema pallidum DNA in their genital lesions by PCR assays using primers that target the bmp, tpp-47, and polA genes. None of the patients without syphilis had positive PCR results. Five molecular subtypes were identified, with 1 type (14f) causing 79% of the cases. All 38 patients were found to be infected with macrolide-resistant strains.

Three common treponemal gene targets (bmp, tpp-47, and polA) were detectable by PCR in patients with primary syphilis. A single clone characterized as 14f and showing macrolide resistance appeared to have caused most of the primary syphilis cases in this study.