Click ES, Kurbatova E, Alexander H, et al. - Given the reports of resistance to anti-tuberculosis (TB) drugs isoniazid and rifampin in presence of mutations in the genes inhA, katG, and rpoB, researchers here examined if specific mutations in these genes were correlated with different clinical and microbiological characteristics. In this multi-country prospective cohort study of MDR-TB, sputum isolates were investigated for inhA, katG and rpoB mutations using the Hain MTBDRplus line probe assay. From January 2005 to December 2008, they enrolled 447 participants from seven countries. Compared with rpoB S531L, isolates with rpoB D516V exhibited less cross-resistance to rifabutin, raised baseline resistance to other drugs, and raised acquired fluoroquinolone resistance. Relative to mutation of katG only, mutation of inhA promoter and katG was correlated with heightened acquired fluoroquinolone resistance and slower time-to-sputum-culture-conversion (TSCC; 125.5 vs 89.0 days). Findings thereby suggest a correlation of specific mutations in inhA and katG with differences in resistance to other drugs and TSCC. They suggest the possible utility of molecular testing in tailoring treatment and assessing additional drug resistance risk according to a specific mutation profile.