RAPID SUSCEPTIBILITY TESTING OF MYCOBACTERIUM-TUBERCULOSIS (H37RA) BYFLOW-CYTOMETRY

The resurgence of tuberculosis has caused considerable effort to be fo cused on the development of rapid methods for determining the suscepti bility of Mycobacterium tuberculosis to antimycobacterial agents. We d emonstrated that susceptibility testing of M. tuberculosis can be acco mplished rapidly by using flow cytometry. Results of tests were availa ble within 24 h after M. tuberculosis organisms were incubated with et hambutol, isoniazid, rifampin, or streptomycin. The method was based o n the ability of viable M. tuberculosis organisms to hydrolyze fluores cein diacetate (FDA) and the detection of fluorescent mycobacteria by flow cytometric analysis, The assay system also did not require multip lication of the mycobacteria. In contrast, M. tuberculosis organisms e xposed to antimycobacterial agents hydrolyzed significantly less FDA. The use of flow cytometry and FDA staining shows considerable promise as a rapid method for obtaining susceptibility test results.