Molecular epidemiology of Treponema pallidum subsp. pallidum among men who have sex with men at an HIV referral hospital in Tokyo: Multilocus sequence typing and macrolide resistance.

Molecular analysis of Treponema pallidum subsp. pallidum is limited by culture difficulties. We conducted a study using prospectively collected clinical whole-blood specime applying multi-locus sequence typing (MLST) to whole blood to assess strain distribution and macrolide resistance in a cohort of primarily men who have sex with men (MSM) at an HIV referral hospital in Tokyo. MLST was successful in 28 cases (26%, n = 28/109) of syphilis between 2019 and 2023; 26 were MSM with HIV. ST3 (n = 11) and ST6 (n = 9) were most common sequence types. The 23S rRNA A2058G mutation was detected in 93% (25/27) of successfully analyzed samples, whereas no A2059G mutations were observed, irrespective of sequence type. Both SS14 and Nichols clades showed high A2058G prevalence. Although the success rate of whole-blood MLST was limited, the approach was implementable and revealed a high prevalence of macrolide resistance in this cohort.