Objectives To determine whether the main 23S rRNA mutation (A2058G) that confers macrolide resistance in Treponema pallidum is present among DNA obtained from syphilitic ulcers in South Africa and to determine the strain subtype distribution using molecular methods.
Methods DNA was re-extracted from sixty ulcer swabs, previously shown to contain T pallidum DNA by in-house real-time multiplex PCR assay, using a MagNA Pure Compact DNA extraction system (Roche, Germany). The genital ulcer specimens were collected in South Africa between 2005 and 2009 during either national microbiological surveillance activities or as part of large episodic acyclovir treatment trial (HSV4294). The re-extracted DNA was screened for the A2058G point mutation in the peptidyltransferase region of the 23S rRNA subunit using a rapid PCR-based restriction digest assay. Subtyping of T pallidum, using a previously-published technique, was based on the molecular characterisation of two variable treponemal repeat genes, arp and tpr.
Results Macrolide resistance profiles and the subtype distribution for all 60 DNA samples were obtained. The mean age of all participants was 27.4 years (range 18–43; SD 5.24) of which 55 (92%) were male and 5 (8%) were female. None of the samples analysed contained the 23S rRNA gene point mutation that confers macrolide resistance. A total of eight arp repeat sizes, 8 RFLP patterns and a combined total of 17 subtypes were identified in this study population. The most common subtypes were 14d (43%), followed by 17d (13%), 14b (7%), 22b (5%) and 23b (5%).
Conclusions This is the first South African study to examine both macrolide-resistance profiles and the subtype distribution of syphilis strains using molecular techniques. Macrolide-resistant T pallidum strains appear to be uncommon in South Africa compared to more developed countries. Our results indicated subtype 14d to be the predominant circulating T pallidum strain in South Africa and there seem to be a high degree of genetic heterogeneity within this population.