The inhibitory action of agar on certain strains of pleuropneumonia-like organisms.

The pleuropneumonia-like organisms (PPLO) are recognized as a group of rather fastidious microorganisms. Various peptones, infusions, and serum supplements have been examined by many investigators relating to the development of a medium satisfactory for the in vitro cultivation of these organisms (Morton et al., 1951; Edward, 1947; and others). However, few reports of examinations of the agar incorporated into the medium are available. While we were encountering difficulties with agar, Liebermeister (1954) encountered somewhat similar experiences in Germany. The present investigation was prompted by the sudden occurrence of severe retardation of growth of some strains of PPLO during routine cultivation of stock strains on culture medium previously found satisfactory. In reviewing the ingredients incorporated into the medium in question, it was found that agar from a different manufacturer had been used. These observations are presented to call attention to the unsuitability of some lots of agar as an ingredient in culture media to be used for the cultivation of PPLO.