Capacity of Abbott RealTi<i>me</i> MTB RIF/INH to detect rifampicin- and isoniazid-resistant tuberculosis

BACKGROUND Abbott RealTi me MTB RIF/INH Resistance (RT RIF/INH) is a new assay for the detection of resistance to rifampicin (RIF) and isoniazid (INH) in tuberculosis (TB) patients. OBJECTIVE To evaluate the capacity of RT RIF/INH to detect resistance-associated mutations in target genes. METHODS A total of 311 Mycobacterium tuberculosis strains that had been pre-characterised using genotypic methods (GenoType ® MTBDR plus , Sanger sequencing) and phenotypic drug susceptibility testing were subjected to DNA extraction on Abbott m 2000 sp and analysed using RT RIF/INH. Detection of heteroresistant mutations was studied with artificial mixtures of wild-type and mutant DNA. RESULTS Overall sensitivity and specificity values of RT RIF/INH to detect resistance were respectively 87.2% and 98.4% for RIF and respectively 90.1% and 99.2% for INH. The capacity of RT RIF/INH to detect specific mutations was 100% for kat G, inh A and frequent rpo B mutations, and 76% for rare rpo B mutations. Among the latter, two rare mutations were not consistently detected. With heteroresistant samples, RT RIF/INH reported resistance if samples contained at least 75-90% of mutant DNA. CONCLUSION RT RIF/INH is a reliable high-throughput assay for the detection of RIF and INH resistance markers. The ability to detect INH resistance also may be of benefit in areas with high rates of INH-resistant, non-multidrug-resistant TB. .