Studies on an untyped avian mycoplasma related to mycoplasma gallisepticum

This thesis describes studies on two related mycoplasma strains (4229 and B2/85) from a duck and partridge respectively. They were originally identified as M. gallisepticum but later serological studies on strain 4229 had revealed only a partial relationship with M. gallisepticum, and DNA:DNA hybridisation showed approximately 40% homology between them, suggesting that the organism is a distinct and possibly new species. The purpose of this study was therefore to characterise strain 4229 according to the recommendations of the International Committee on Systematic Bacteriology Subcommittee on the Taxonomy of Mollicutes to establish it as a new species. Strain B2/85 was also included for comparison.

Restriction endonuclease analysis of the DNA of strains 4229 and B2/85 with three enzymes failed to show any differences between them, although they differed from M. gallisepticum strains S6 and PG31. Light and electron microscopy revealed a pleomorphic nature and absence of a cell wall. Both strains possessed a triple-layered membrane and a terminal tip-like organelle resembling that of M. gallisepticum. There was no evidence of helical forms. The organisms were not obligate anaerobes, they produced colonies typical of Mollicutes and L-phase bacteria, but there was no reversion to bacterial forms on passage in medium without bacterial inhibitors. Both strains passed through membrane filters of 450 and 220 nm pore diameter. They were therefore described as members of class Mollicutes, but excluded from the order Anaeroplasmatales and from the family Spiroplasmataceae.

Sensitivity to digitonin and sodium polyanethol sulphonate gave indirect evidence of a sterol requirement, excluding the organisms from the order Acholeplaematales. They were thus assigned to the order Mycoplasmatales, family Mycoplasmataceae. Since they did not hydrolyse urea they were placed in the genus Mycoplasma.

Biochemical tests were carried out to provide a species description. Both strains showed the same properties as M. gallisepticum. They were glucose positive, but negative for arginine hydrolysis, phosphatase activity, film and spots production and liquefaction of serum.