Abstract
In total, 49 clinical samples were analyzed using two typing schemes, Enhanced Centers for Disease Control and Prevention (ECDC) and multilocus sequence typing (MLST), to describe the molecular characteristics of circulating Treponema pallidum isolates in Xiamen between 2016 and 2017. In addition, genetic mutations potentially related to antibiotic resistance of T. pallidum were also analyzed. Forty five samples were fully typed by ECDC, and 14 different subtypes were detected. The most common subtype was 16d/f (24.4%), followed by 14d/f (20.0%). All forty nine samples were successfully typed by MLST, while only four allelic profiles were identified, including three SS14-like profiles and one Nichols-like profile. Among them, the major allelic profile was 1.1.8 (85.7%). Interestingly, the allelic profile 1.3.1 widespread in Europe and North America was not detected in this region. Additionally, A2058G mutation in 23S rRNA was found in all detectable samples (38/38), and no mutation in 16S rRNA was observed (36/36). Four non-synonymous single-nucleotide polymorphisms in penicillin-binding protein genes were found in the 35 samples eligible for Sanger sequencing. Among them, the variant in tp0500 (P564I) can only be found in the SS14-like isolates. Homoplastic changes in tp0760 (I415F/I415M) and tp0705 (A506V/A506T) were found. Moreover, the variant tp0705 A506V and the variant tp0705 A506T separately appeared in the SS14-like isolates and Nichols-like isolates, respectively. This study showed that the genotypes of T. pallidum isolates in Xiamen between 2016 and 2017 were different from those in other geographic areas. The resistance-related variants of T. pallidum isolates identified in this study could provide awareness for clinicians in the treatment of syphilis.
Highlights
Syphilis, caused by Treponema pallidum subsp. pallidum, is a chronic sexually transmitted disease
We explored the 23S rRNA gene, 16S rRNA gene and three penicillin-binding protein genes for potential mutations associated with antibiotic resistance in the T. pallidum isolates
According to the US Centers for Disease Control and Prevention (CDC) and the European CDC (ECDC) guidelines (Janier et al, 2014; Workowski and Bolan, 2015), syphilis patients were clinically diagnosed based on clinical findings with laboratory tests including serological tests and dark-filed microscopy
Summary
Syphilis, caused by Treponema pallidum subsp. pallidum, is a chronic sexually transmitted disease. With the prevalence of SS14-like strains worldwide, one of the two main T. pallidum clades, sequencing-based molecular typing was supplemented with additional sequencing of the tp0705 gene, known as the multilocus sequence typing (MLST) system, to greatly increase the genotype resolution power for SS14-like isolates (Grillova et al, 2018). The typing scheme based on direct sequencing of typing loci effectively improved the success rate of fully typed isolates and ensured stability. It enabled the construction of phylogenetic trees to trace infections and distinguish T. pallidum from other treponemal subspecies (Grillova et al, 2018; Grillova et al, 2019a)
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