Aids for in vitro Mycobacterium lepraemurium investigations: estimation of oxidation-reduction potentials and pO2 with 2, 6 dichlorophenol indophenol.

The partial success in cultivating a "host-dependent" microbe provided the incentive to develop methods which may aid the growth of the organism. The oxidation-reduction potential (ORP) of NC-5, an aerobic, cysteine containing medium which supports the limited in vitro growth of Mycobacterium lepraemurium, is measurable with the redox dye, 2, 6 dichlorophenol indophenol. Both cysteine and autoclaved glucose can be used to adjust to ORP. Glucose autoclaved in phosphate buffer but not in aqueous solutions reduced the dye. The dye was also reduced in glucose solutions by atmospheres containing 10% and 1%-2% pO2. With exposure to 20% pO2 the reoxidation of the dye was slow but complete. Thus, the dye in glucose solutions provides a general method for estimating pO2 above the level of anaerobiosis. Proper adjustment and monitoring of the ORP and pO2 may enhance growth.