Comparative In Vitro Growth Analysis of Seven Syphilis-Causing Treponema pallidum Strains

We analyzed in vitro growth rates of seven Treponema pallidum subsp. pallidum strains, three Nichols-like (DAL-1, Madras, Haiti B) and four SS14-like (Mexico A, SS14, Grady, Philadelphia 1). During three week-long binary co-cultivations of seven TPA strains (n = 21), significantly different growth rate was confirmed for individual strains using PCR amplicon sequencing of genomic regions differentiating TPA-pairs. While the generation time of strain DAL-1 was 32.97 hours, the slowest strain, Philadelphia 1, had generation time 43.5 hours. These findings highlight notable physiological differences that may relate to variations in syphilis clinical presentation.