Complement-mediated killing of Ureaplasma urealyticum by antibody directed against components of the growth medium

Many strains of Ureaplasma urealyticum were inactivated, in the presence of complement, by a control antiserum prepared in guinea-pigs against the uninfected culture medium used to grow ureaplasmas. This mycoplasmacidal activity of the control serum, unlike that of the specific antisera prepared against the organisms themselves, was removed by treatment with dithiothreitol or by absorption with the horse-serum component of the medium, suggesting that the activity was due to an antibody of the IgM class acting on horse-serum proteins that had become associated with the surface of the ureaplasmas. The mycoplasmacidal activity in the specific ureaplasma antisera appeared to be due mainly to antibody of the IgG class. A similar complement-dependent mycoplasmacidal antibody to U. urealyticum apparently active against serum components, was present in normal rabbit sera.