Secreted sialidase activity of canine mycoplasmas.

Through a survey of the phylogenetic distribution of sialidase among mycoplasmas, we detected activity secreted by the type strains of 3 of 11 species frequently or first isolated from dogs. The specific activity of washed cells of the type strains of Mycoplasma canis, Mycoplasma cynos, and Mycoplasma molare ranged from 5.2+/-0.8 x 10(-6) to 1.1+/-0.3 x 10(-5) enzymatic units per colony-forming unit (U/CFU). Cells of M. molare strain H542(T) had twice the specific activity (P<0.05) of M. canis strain PG14(T) or M. cynos strain H831(T). Significant differences in sialidase activity existed among nine clinical isolates of M. canis, ranging from not detectable to 2.1+/-0.1 x 10(-5)U/CFU. The type strains of other species previously isolated from dogs (Mycoplasma arginini, Mycoplasma bovigenitalium, Mycoplasma edwardii, Mycoplasma felis, Mycoplasma gatae, Mycoplasma maculosum, Mycoplasma opalescens, and Mycoplasma spumans) did not exhibit either secreted or cell-associated sialidase activity. Neither specific nor degenerate PCR primers complementary to the three known mycoplasmal sialidase alleles were able to amplify orthologs in M. canis, M. cynos, or M. molare, further evidence that the secreted sialidase of those species is distinct from the strictly cell-associated sialidases of Mycoplasma alligatoris, Mycoplasma synoviae, and Mycoplasma gallisepticum. This is the first report of a well-known bacterial virulence factor whose expression varies among strains of certain Mycoplasma species that infect dogs.