RAPID SUSCEPTIBILITY TESTING FOR NONTUBERCULOSIS MYCOBACTERIA USING FLOW-CYTOMETRY

We demonstrated previously that susceptibility testing of Mycobacteriu m tuberculosis could be accomplished within 24 h after the organisms w ere incubated with antituberculosis agents by using fluorescein diacet ate (FDA) staining and flow cytometry. Continued studies have now show n that assay suspensions containing M. avium, M, fortuitum, M, gordona e, or M, marinum incubated with various concentrations of ciprofloxaci n, clarithromycin, erythromycin, kanamycin, rifampin, and tobramycin h ydrolyzed less FDA than drug-free controls. Suspensions of treated and nontreated mycobacteria could be easily differentiated at 6 and 24 h after the initiation of the susceptibility assays by using FDA stainin g and flow cytometry. In addition, multiplication of the mycobacteria was not required to discern differences between drug-free suspensions of mycobacteria and those treated with antimycobacterial agents. The f low cytometric assay is simple, reproducible, and rapid.