Selective action of thallium acetate and crystal violet for pleuropneumonialike organisms of human origin.

The prevalence of pleuropneumonialike organisms (PPLO) has been summarized by Morton et al. (1952). Their incidence and significance in infections of the genitourinary tract have been discussed by Ruiter and Wentholt (1953a) and Edward (1952). Subsequent reports of the finding of these organisms in infections of man (Slingerland and Morgan, 1952; Ruiter and Wentholt, 1953b) and of poultry (Markham and Wong, 1952; Grumbles et al., 1953) increase the importance of searching for these organisms in suspected infectious diseases. The culture medium for the isolation and propagation of pleuropneumonialike organisms has to be highly nutritive, and an incubation period of from three to five days is required. Under these conditions it is often difficult and sometimes impossible to exclude bacteria. It is highly desirable, therefore, to be able to inhibit a wide variety of bacterial species but, at the same time, permit growth of pleuropneumonialike organisms. That the metabolism of pleuropneumonialike organisms isolated from man may be different from that of bacteria in general is suggested by the work of Smith et al. (1950). These authors observed that pleuropneumonialike organisms behaved neither like gram positive nor gram negative organisms. They were not inhibited by 1:50,000 concentration of potassium tellurite which suppresses growth of most gram negative microorganisms nor by crystal violet in a concentration of 1:100,000 which suppresses growth of most gram positive microorganisms. The crystal violet can be added to the culture medium before sterilization, but the potassium tellurite does not withstand autoclaving and has to be added aseptically to the sterile medium.