Occurrence of rpoB mutations in isoniazid-resistant but rifampin-susceptible Mycobacterium tuberculosis isolates from Germany

Abstract

Four out of 143 phenotypically isoniazid-resistant but rifampin-susceptible Mycobacterium tuberculosis strains that were isolated from patients in Germany in 2011 had mutations in the rifampin resistance-determining region of rpoB. After performing drug susceptibility testing (DST) with two methods, the proportion method on Löwenstein-Jensen medium and using the Bactec 960 Mycobacteria Growth Indicator Tube system, we conclude that the two methods are equally reliable for phenotypic DST and MIC determination.

FIG 1

RMP MICs below the critical concentrations determined by the Bactec 960 MGIT system and the proportion method on LJ medium. Only the concentrations tested, beginning with 2.5 μg/ml, are given on the y axes. The adjusted critical concentrations for the two methods (LJ medium, 40 μg/ml; Bactec 960 MGIT, 1 μg/ml) are represented by a dashed line.