Chapter 7.8 : Susceptibility Testing by Agar Proportion Method for Mycobacterium tuberculosis Complex

Abstract:

Antimicrobial susceptibility testing should be performed on each patient’s initial Mycobacterium tuberculosis complex isolate, in relapse or re-treatment cases, and when acquired drug resistance is suspected. The modified agar proportion method is used to determine the susceptibility of M. tuberculosis complex, indirectly from a pure culture. Quadrant plates are used that contain either Middlebrook 7H10 agar without antimicrobial agents (control plate) or 7H10 agar with antimicrobial agents at various concentrations (testing plates). Most of primary antituberculosis drugs (i.e., isoniazid [INH], ethambutol [EMB], and rifampin [RIF]) and second-line drugs can be tested with this method. Pyrazinamide (PZA), however, cannot be tested by this method.