Assessing the viability of Mycobacterium leprae by the fluorescein diacetate/ethidium bromide staining technique

In the present study we have evaluated the Fluorescein Diacetate/Ethidium Bromide (FDA/EB) staining technique to assess the viability of Mycobacterium leprae obtained from biopsies of leprosy patients under different periods of treatment. Bacillary suspensions were obtained from skin punch biopsies and stained with the FDA/EB solution. The average percentage of green cells seen which were deemed to be viable were: 67.2% of green cells in patients without previous treatment; 45.6% in patients with 1 to 6 months of treatment; 25.9% for patients with 7 to 12 months of treatment and 10.5% in patients with 13 to 24 months of treatment. All the patients studied were on multidrug therapy. The differences obtained in the percentages of green cells in the different groups of patients were statistically significant as determined by the Wilcoxon's test. The decrease in the percentage of green cells observed with increasing periods of treatment suggests that the FDA/EB technique correlates with the actual viability of M. leprae. The application of this technique in the routine procedures performed with Hansen's disease patients could be very useful for monitoring the effectiveness of treatment in leprosy patients.