Molecular Typing Characterization Of Treponema Pallidum Based On ECDC And MLST Typing Schemes And Antibiotic Resistance-related Genes In Xiamen

Background:The increased prevalence of syphilis in China prompted us to describe the molecular characteristics of circulating T.pallidum isolates and antibiotic resistance-related genes of T.pallidum in Xiamen.We used two typing schemes,ECDC and MLST,to study T.pallidum collected from 2016 to 2017.Methods:A total of 78 clinical samples were collected between 2016 and 2017,49 of which showed tp0574-positive.Two typing schemes,ECDC and MLST,were applied.Gene mutations that are potentially related to antibiotic resistance of T.pallidum isolates,including those in the 23S rRNA gene,16S rRNA gene and three penicillin-binding protein(pbp)genes(tp0500,tp0760 and tp0705),were also analyzed by Sanger sequencing.Results:There were 45 samples fully typed by the ECDC typing scheme,and 14 different subtypes were detected.The common subtype in Xiamen between 2016 and 2017 was 16d/f(24.4%),and the previously prevalent subtype 14d/f(20.0%)in other regions was the next most prevalent.In contrast to the ECDC typing scheme,the MLST approach successfully typed all 49 samples,while only four allelic profiles were identified,including three allelic profiles(1.1.8,1.56.8,1.57,8)belonging to the SS14-like group and one allelic profile(3.2.3)belonging to the Nichols-like group.Among them,the major allelic profile was 1.1.8(85.7%),which belongs to the SS14like group.Interestingly,the allelic profile 1.1.3 that was widespread in Europe and North America was not detected in this region.Additionally,the A2058G mutation in 23S rRNA was present in all detected samples(38/38),and no mutation in 16S rRNA was detected(36/36).Thirty-five samples were analyzed,and four nonsynonymous single-nucleotide polymorphisms in pbp genes were found.Among them,the variant in tp0500(P564I)was exclusively present in the isolates belonging to the SS14-like group,and homoplastic changes in tp0760(I415F/I415M)and tp0705(A506V/A506T)were found.Moreover,the variant tp0705 A506V only appeared in the SS14-like isolates,and the variant tp0705 A506T only appeared in the Nicholslike isolates.Conclusion:Four allelic profiles(MLST)and fourteen subtypes(ECDC)were identidied in Xiamen between 2016 and 2017,and 1.1.8(85.7%)or 16d/f(24.4%)was prevalent genotype.The prevalent genotype of T.pallidum isolates in Xiamen was different from that in other geographic areas,demonstrating the dynamic syphilis epidemiology and syphilis evolution.All of T.pallidum isolates had A2058G mutation and had not A2059G mutation in 23S rRNA;16S rRNA were wild-type;four nonsynonymous SNPs had been found in pbp genes,although the significance of these SNPs had not been determined.Identifying genetic mutations associated with antibiotic resistance of T.pallidum isolates could provide good awareness for clinicians in the treatment of syphilis.