Contact-independent cytotoxicity of Trichomonas vaginalis.

OBJECTIVE To test the dependency of haemolytic and cytocidal manifestations of pathogenicity of Trichomonas vaginalis on direct contact between the target cells and the organism. TEST ORGANISM: T vaginalis strain Baltimore 42. DESIGN Haemolysis in the presence of live T vaginalis and of its filter-sterilised metabolic products was compared. The dependence of haemolytic and cytocidal effects on retention of low pH of metabolic products of the organism was demonstrated by parallel titrations of sterile filtrates in normal saline and in phosphate buffered saline (PBS) pH 7.0. RESULTS Near complete lysis was obtained when erythrocytes mixed with T vaginalis were incubated for 1 h at 37 degrees C in saline containing 1% glucose. The same degree of haemolysis was present in filter-sterilised glucose-saline in which the organism was incubated (1 h/37 degrees C) before erythrocytes were added and incubated under the same conditions as in the mixture with the organism. The degree of haemolysis in filtrates was dependent on retention of low pH (below 5.0) of the suspending fluid in which the organism alone was incubated. Dilution of filtrates in PBS, as opposed to normal saline, abolished or diminished the haemolytic effect. Presence of glucose (energy source) in the saline during incubation of the organism had a pronounced enhancing effect. The production of haemolytic metabolites was temperature dependent, whereas the haemolytic process per se was not. The effect was not an exclusive property of T vaginalis since it was also demonstrated with other trichomonads. The same filtrates applied to tissue culture exerted cytocidal effect strikingly similar to that observed in the haemolysis experiments. CONCLUSION Neither haemolytic nor cytocidal effect of T vaginalis was contact-dependent.