A comparison of the virulence of three strains of Mycoplasma gallisepticum and one strain of Mycoplasma gallinarum in chicks, turkey poults, tracheal organ cultures and embryonated fowl eggs.

The virulence of three strains of Mycoplasma gallisepticum (S6 of low broth passage, S6 of high broth passage and A514) and of one strain of M gallinarum was investigated in specific pathogen free chicks, turkey poults, chick embryo tracheal organ cultures and embryonated fowl eggs. One strain of M gallisepticum, S6, of low passage, caused high mortality in newly hatched chicks, and turkey poults, high embryo mortality, and rapid suppression of ciliary activity in tracheal organ cultures. The other strains of M gallisepticum and M gallinarum had relatively less effect. In view of its greater sensitivity, chick embryo mortality is preferable to tracheal organ culture for assessing the virulence of experimental strains of M gallisepticum.