In vitro and in vivo properties of chemically induced temperature-sensitive mutants of Chlamydia psittaci var. ovis: screening in a murine model.

Two temperature-sensitive (ts) strains, 1B and 1H, were obtained after nitrosoguanidine treatment of the wild-type virulent abortive ovine strain Chlamydia psittaci AB7. Optimum growth temperature on McCoy cells was 38 degrees C for the three strains, but at the restrictive temperature, 39.5 degrees C, ts strains differed from the parental strain in their total infective yield of chlamydiae, their efficiency of plating, and the morphology of the plaques and cytoplasmic inclusions. Their survival at 51 degrees C was also reduced compared with that of the wild field strains. The virulence of the two ts strains was attenuated for pregnant mice, but these two ts strains were able to multiply in mice and to induce a strong immunity to virulent challenge with either the parental AB7 strain or the caprine or bovine abortive field strains.