Viability of Mycobacterium leprae: a comparison of morphological index and fluorescent staining techniques in slit-skin smears and M. leprae suspensions.

In a comparison of the estimation of Mycobacterium leprae viability by morphology and the fluorescent vital dyes FDA/EB and R123/EB, the latter techniques were more satisfactory using suspensions and slit-skin smears of M. leprae bacilli. Both FDA/EB and R123/EB seem to more accurately reflect viability after freeze/thaw cycles and heating, and are able to detect lower percentages of viable bacilli. In addition, the fluorescent vital dye techniques are both simple and less open to subjective interpretation than the conventional estimation of the morphological index.