Mycoplasma Species Identification Based upon Growth Inhibition by Specific Antisera

Summary A method of mycoplasma species identification is described, based upon inhibition of the PPLO growth on solid media around antiserum-impregnated filter paper disks. In comparison to the classical serologic identification method using complement fixation, the technique described was completely species-specific for identification of unknown antigens, but was less sensitive for detection of antibodies in sera. Examination of several variables influencing this reaction indicated that factors relating to the ratio between the number of organisms used and the amount of antiserum were more important determinants than were factors concerned with antiserum diffusion through the media. The ability of the antisera to produce growth inhibition by the means described was a stable property, being retained after long periods of storage at -20°C and 4°C, and after heating at 56°C. Application of the inhibition technique permitted successful identification of 150 pleuropneumonia-like organisms (PPLO) isolated from the human pharynx in health and disease, and five strains recovered from tissue cultures. The method was simpler to perform and to interpret than species identification based upon the complement fixation technique. In the course of these studies, a PPLO isolated frequently from the normal human pharynx was defined which was distinct from the classified mycoplasma species of human derivation by both the complement fixation and growth inhibition methods. This emphasizes the need for recognition of this and other ubiquitous PPLO species by investigators studying human respiratory tract disease.