f Mycoplasma subdolum, a New Species Isolated from Horses

The growth characteristics, biochemical activities, and serological relationships of a group of mycoplasmas that were originally described as capable of splitting urea were reexamined. Most of the strains examined were isolated from the genital tract of mares and stallions or from the tissues of aborted equine fetuses, but one was obtained from the respiratory tract and another was obtained from the brain of a horse. The colonial morphology and growth characteristics of these isolates were those of the classical “large-colony” mycoplasmas rather than those of species of Ureaplasma. The mycoplasmas hydrolyzed arginine, were inhibited by sodium polyanethol sulfonate and digitonin, and failed to grow without cholesterol. Thus, they had the properties of a typical arginine-degrading species of Mycoplasma. The strains produced a slow but restricted increase in the pH of some types of urea-containing broth, but these pH changes were smaller and less rapid than those given by strains of Ureaplasma. Apart from these properties, the strains were unremarkable in their biochemical activities, although they could be distinguished from strains of M. equirhinis, an arginine-degrading species found in horses, by their failure to produce “film and spots” on serum-containing media. The serological results and electrophoresis of cell proteins suggest that the strains examined constitute a fairly homogeneous group. A representative strain, TB, was shown to be serologically distinct from strains of 48 species of Mycoplasma and of 3 species of Acholeplasma. These species included 8 found in horses and 24 which metabolized arginine or arginine and glucose. On the basis of these results, it is suggested that strain TB and related strains constitute a new species, for which the name Mycoplasma subdolum is proposed. Strain TB (= NCTC 10175 = ATCC 29870) is the type strain.