Reduction of tetrazolium salts by pleuropneumonialike organisms.

Tetrazolium salts have proved useful as indicators of electron transfer. Compounds such as triphenyltetrazolium chloride' are more practical than indicators like methylene blue since they are converted from a soluble colorless salt to an insoluble formazan in the reduced state. They also provide similar convenience in detecting enzymatic activity and specific sites of such activity (Bielig, Kausche, and Haardick, 1949; Mudd et al., 1951). Pleuropneumonialike organisms (PPLO) are characterized by the small size of the colonies, their fragility, poor staining qualities, slow rate of growth, and requirement of a high concentration of native protein for growth in vitro. It is not surprising that there are few data on the metabolic properties of these organisms. However, use of newer, simplified culture medium (Morton, Smith, and Leberman, 1951; Smith and Morton, 1951) and improved indicators may permit the resolution of the pathways involved in the metabolism and respiration of pleuropneumonialike organisms. It was apparent that demonstration of enzymatic activity in pleuropneumonialike organisms might be obtained through the use of the tetrazolium compounds since the colonies gave visible evidence of oxidative metabolism through the reduction of tetrazoles which had been incorporated into the culture media.