Inhibition of Growth of Mycoplasma mycoides by Bovine Serum

Fresh bovine serum containing complement-fixing antibody to Mycoplasma mycoides reduced the log10 of the viable count of a liquid culture of the organism incubated in its presence by 1 to 4. As heating of the serum at 56°C.for 30 minutes destroyed this activity, it was concluded that the presence of a heat-labile factor was essential; it is assumed that this is complement. In addition, a heat-stable factor was shown to be required; this factor was present also in sera from many cattle that had not been exposed to M. mycoides infection and with no antibody to that organism detectable in complement-fixation or agglutination tests. As this factor could be removed by absorption with M. mycoides but not with serologically unrelated strains of Mycoplasma, not only from known M. mycoides antisera, but also from those inhibitory sera with no detectable antibody, it is assumed that the heat-stable factor is a relatively specific antibody to M. mycoides, reactive in minute amounts. It is suggested that these 2 factors, together with bovine conglutinin, cause an aggregation, and that it is this aggregation of the organism that may greatly reduce colony counts made to measure viability.