Reversion of a Pleuropneumonia-like Organism to a Corynebacterium during Tissue Culture Passage

SUMMARY: A strain of a pleuropneumonia-like organism (PPLO) isolated from urethral exudate from a case of non-specific urethritis was studied in HeLa cell tissue cultures. Although the organisms entered the cell cytoplasm, they did not produce marked damage or proliferate luxuriantly until filtrate from a broth culture of Staphylococcus pyogenes or yeast extract was added to the infected tissue cultures. The organisms subsequently isolated from tissue cultures initially inoculated with PPLO and yeast extract showed conversion from PPLO form to L form of growth. Further culture of the L form, especially with the aid of mucin, resulted in conversion of the L form to a corynebacterium. This corynebacterium was indistinguishable culturally, biochemically and serologically from a corynebacterium isolated on rabbit blood agar plates which had been inoculated with a portion of the original urethral exudate from the same case of non-specific urethritis. The view is expressed that other human genital strains regarded at present as PPLO may be found to be L forms of Corynebacterium spp. The criteria for identification of PPLO and L forms are discussed.