Mycoplasma fastidiosum: a New Species from Horses

Abstract

The morphology, growth characteristics, biochemical activities, and serological relationships of a group of eight slow glucose-metabolizing mycoplasmas isolated from nasopharyngeal swabs from horses are described. Representatives of the group possessed a triple-layered limiting membrane and had the essential cultural and biological properties of mycoplasmas. They were highly filamentous, but unusual morphological features were the twisting of the filaments and the regular diagonal striations revealed by electron microscopy. Also notable were the somewhat fastidious nutritional requirements of the slow glucose-metabolizing mycoplasmas and their susceptibility to erythromycin (0.1 μg/ml). Serologically, a representative strain, 4822, was distinct from strains of 58 species of Mycoplasma and of Spiroplasma citri when tested by the disk growth inhibition test or the indirect fluorescent-antibody test. A cross-reaction with certain strains of M. pulmonis was detected in some growth inhibition tests on a medium (LH agar) subsequently shown to be suboptimal for growth. Comparison of 4822 with several strains of M. pulmonis in growth inhibition, metabolism inhibition, and indirect fluorescent-antibody tests with HuS medium failed to show any cross-reactions. Thus, serological methods based on inhibition of growth or metabolism must be used with caution when identifying nutritionally fastidious mycoplasmas that are likely to be inhibited by nonspecific factors. The evidence presented here suggests that the slow glucose-metabolizing strains constitute a new species, for which the name Mycoplasma fastidiosum is proposed. Strain 4822 (= NCTC 10180) is the type strain.