In vitro Antimicrobial Susceptibility of Treponema pallidum subsp. pallidum

Using the recently described culture system for T. pallidum, we exposed the pathogen to a concentration range of each tested antibiotic. After 7 days, the treponemal burden was evaluated by qPCR targeting the T. pallidum tp0574 gene. The primary outcome was the Minimum Inhibitory Concentration (MIC), at which the mean number of tp0574 copies was not significantly higher than the inoculum wells. We also investigated the susceptibility of macrolide-resistant strains to high concentrations of azithromycin, and the possibility of developing resistance to linezolid, a recently proposed candidate for syphilis treatment.