The Assessment of Viability ofM. Tuberculosisafter Exposure to CPC Using Different Methods

Settings. National Institute for Research in Tuberculosis, Chennai.Objective. To assess the proportion of metabolically active cells ofMycobacterium tuberculosisafter exposed to CPC using FDA-EB vital staining and viable counts on LJ medium. Mycolic acid content inM. tuberculosisafter exposure to CPC was estimated using HPLC.Methods. Clinical isolates ofM. tuberculosisand standard reference strainM. tuberculosisH37Rv were used for FDA-EB, viable count, and HPLC.Results. FDA/EB consistently stained 70–90% of log phase cells as green and the remaining cells as red-orange. After CPC treatment, 65–70% of the cells stained red-orange. The viability counts were comparable to 0-day controls. Synthesis of mycolic acids in mycobacteria was reduced when exposed to CPC using HPLC due to the decreased metabolic activity of the organisms.Conclusion. The cells are metabolically inactive during storage with CPC but these cells grew well on LJ medium after removal of CPC. The viability ofM. tuberculosiswas maintained in CPC with minimal reduction. Mycolic acid content was reduced if the cells ofM. tuberculosiswere treated with CPC for 7 days. All the above findings provide yet another evidence for the damage of cell wall ofM. tuberculosis.