Factors Influencing Growth Inhibition of Mycoplasma pneumoniae By Immune Sera. ∗

Summary

Studies on growth inhibition of M. pneumoniae revealed three interdependent major variables: number of organisms used in titrations, amount of antiserum, and time of test incubation. A linear relationship between the logarithms of the number of organisms inhibited and the antiserum dilution was observed in which the regression ratio was 2.0. Heat-labile factors in normal sera, required for inhibition of M. pneumoniae, were readily provided by incorporating fresh frozen horse serum into the growth medium. Other animal sera could not be used because of the presence of heat-labile inhibitors; commercial guinea pig “complement” additionally contained 2 heat-stable inhibitors, specific antibody and sodium azide. Control of the factors indicated provided means of producing immune inhibition measurements of varying sensitivity which were reproducible within a 4-fold range at the 95% confidence level.