Susceptibility of Treponema pallidum and other selected spirochaetes to zidovudine.

The antiviral nucleoside derivative zidovudine (3'-azido-3'-deoxythymidine) previously has been shown to be an effective antibacterial agent in animals infected with Escherichia coli or Salmonella typhimurium. Since HIV infection can alter the course of human syphilis with serious consequences, it was of interest to determine if the noncultivable spirochaetal agent of syphilis, Treponema pallidum, is susceptible to this compound. The progression of experimental rabbit syphilis over a three week period was unchanged in animals receiving either 50 or 150 mg/kg oral zidovudine daily. In addition, a number of cultivable pathogenic and nonpathogenic spirochaetes were tested for susceptibility to zidovudine in vitro. At a concentration of 100 mg/L, zidovudine had no detectable effect on spirochaete growth, morphology, or motility. Thus it appears that spirochaetes are generally not susceptible to this compound, and that long-term zidovudine therapy will not be of benefit in preventing or controlling syphilis or other spirochaetoses in HIV-infected humans receiving this drug.