Long-term in vitro exposure ofTreponema pallidumto sub-bactericidal doxycycline did not induce resistance: Implications for doxy-PEP and syphilis

Abstract

ABSTRACTDoxycycline post-exposure prophylaxis (doxy-PEP) could significantly reduce syphilis incidence. However, the increase in intermittent doxycycline usage might select resistantTreponema pallidum(T. pallidum) strains. To assess whether resistance to doxycycline could be induced in this pathogen, we exposed the SS14 strain in vitro both intermittently and continuously to a sub-bactericidal doxycycline concentration that still exerts antibiotic pressure. During and after each exposure experiment, we assessed the doxycycline minimal inhibitory concentration in test and control treponemes and performed whole genome sequencing, concluding that no resistance developed. This work suggests that doxycycline-resistantT. pallidumis not an immediate threat for doxy-PEP implementation.