Fresh isolates of Trichomonas vaginalis were examined for reactions to a panel of five monoclonal antibodies (MAbs). Four MAbs (C20A3, DM126, DM116, and C55) were to distinct surface immunogens and one MAb (L64) was to a cytoplasmic component. The fresh isolates were evaluated by indirect immunofluorescence (IF), immunoblotting, and radioimmunoprecipitation. IF assay with C20A3 MAb gave isolates which were homogeneous nonstaining (negative [Neg] phenotype) and isolates which were heterogeneous staining and nonstaining (positive [Pos] and Neg phenotype, respectively) organisms. Immunoblotting and radioimmunoprecipitation assays revealed that surface phenotypic heterogeneity among isolates with C20A3 MAb was due to the presence or absence of the immunogen from the parasite surface. IF assay with DM126 MAb also gave Pos and Neg phenotypes among parasites of some isolates. All of the isolates were always Neg phenotype with DM116 and C55 MAbs. The occurrence of Neg phenotype organisms with DM126, DM116, and C55 was due to epitope inaccessibility to their respective MAbs and not to the absence of the immunogen from trichomonal membranes. All isolates possessed the cytoplasmic protein recognized by L64 MAb. Paired isolates (taken 5 to 6 days apart) from 24 women were also studied. Four of the 24 paired isolates (16%) had different phenotype distributions at the two timepoints for C20A3. Fresh isolates also underwent phenotypic variation during in vitro growth and multiplication, as determined with C20A3. Also, 7 of the 24 paired isolates demonstrated dramatic changes in the accessibility of DM126 MAb to epitope binding. Lastly, 55 (90%) of 60 serum samples from patients with trichomoniasis evaluated in this study possessed antibody to the C20A3 reactive molecule. The data show that the fresh T. vaginalis isolates were predominantly Neg phenotype and confirm the occurrence of protein and epitope phenotypic variation for major immunogens among fresh isolates of the pathogenic human trichomonads.

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Six isolates of a strain (MRP-MT) of Trichomonas vaginalis obtained from a woman before and after unsuccessful treatment with metronidazole had an appreciably lower susceptibility to metronidazole both in vitro in the aerobic tube assay and in vivo in the mouse assay than did control strains from patients cured with standard doses of the drug. Our results support recent evidence that metronidazole-resistant strains of T vaginalis do cause treatment failure. Resistance of these strains could be detected in vitro under only aerobic but not anaerobic conditions. The prevalence of metronidazole-resistant strains of T vaginalis should be kept under surveillance in order to estimate their clinical importance. The patient harbouring the resistant strain MRP-MT was finally cured with increased doses of ornidazole.