Molecular and Growth-Based Drug Susceptibility Testing of Mycobacterium tuberculosis Complex for Ethambutol Resistance in the United States.

Ethambutol (EMB) is used as a part of drug regimens for treatment of tuberculosis (TB). Susceptibility of Mycobacterium tuberculosis complex (MTBC) isolates to EMB can be discerned by DNA sequencing to detect mutations in the embB gene associated with resistance. US Public Health Laboratories (PHL) primarily use growth-based drug susceptibility test (DST) methods to determine EMB resistance.

DNA sequencing for confirmation of rifampin resistance detected by Cepheid Xpert MTB/RIF assay.

DNA sequencing of rpoB and culture-based drug susceptibility results were evaluated for samples referred for confirmation of rifampin resistance detected by the Cepheid Xpert MTB/RIF assay. Silent mutations and mutations associated with low-level resistance were found in the study population. These data support CDC recommendations to confirm Xpert rifampin resistance results.