Zinc sensitivity of Trichomonas vaginalis: in vitro studies and clinical implications

The high zinc concentration (2.3-15.3 mM) in human prostatic secretions may be an important defense of the male lower urinary tract against infection by Trichomonas vaginalis. Trichomonads were rapidly killed by zinc salts at concentrations similar to those in prostatic fluid of normal men. There was some variation in the zinc sensitivity of 15 clinical isolates of T. vaginalis (minimal inhibitory concentration, 0.8-6.4 mM). A time-kill technique showed subtle differences in the kinetics of zinc killing of trichomonad strains. It was possible to select relatively zinc-resistant substrains of T. vaginalis from a zinc-sensitive population. Zinc resistance was a stable characteristic after multiple passages of substrains in growth medium without supplemental zinc. Variations in the zinc sensitivity of infecting T. vaginalis strains or in the zinc content of host prostatic secretions may be significant determinants of the natural history of T. vaginalis infection in men.