ANTIOXIDANT DEFENSES IN THE MICROAEROPHILIC PROTOZOAN TRICHOMONAS-VAGINALIS - COMPARISON OF METRONIDAZOLE-RESISTANT AND SENSITIVE STRAINS

The sensitivity of the microaerophilic protozoan Trichomonas vaginalis to oxygen and products of its reduction, and the antioxidant defences employed by this organism, were investigated. Studies revealed that t his amitochondrial flagellate is sensitive to oxygen tensions above th ose experienced in situ in the vagina(i.e. > 60 mu M) and that metroni dazole-resistant strains (CDC 85 and IR78) were more sensitive to elev ated oxygen levels than a metronidatole-sensitive isolate (1910). In t he presence of radical scavengers, inactivation of organisms at 60 mu M oxygen was significantly lessened. Investigation of the antioxidant enzymes present in this organism revealed that activities of peroxide- reducing enzymes (e.g. catalase and general peroxidase) were not detec table, but that a cyanide-insensitive, azide-sensitive superoxide dism utase was present in cell extracts. Measurement of thiol-cycling enzym es indicated that NADPH could drive the reduction of oxidized glutathi one (thiol reductase); however, the corresponding peroxidase activity was not detected. Analysis of thiols in whole cells of T. vaginalis in dicated that glutathione was absent, but high levels of other thiols, propanethiol, methanethiol and H2S, were present. No significant diffe rences were detected in thiol levels or antioxidant enzyme activities on comparison of metronidazole-sensitive and resistant strains. These results indicate that the sensitivity of T. vaginalis to oxygen above physiological levels is due to the lack of adequate peroxide-reducing enzymes and radical-scavenging mechanisms.