Evaluation of the TB-Biochip oligonucleotide microarray system for rapid detection of rifampin resistance in Mycobacterium tuberculosis.

The TB-Biochip oligonucleotide microarray system is a rapid system to detect mutations associated with rifampin (RIF) resistance in mycobacteria. After optimizing the system with 29 laboratory-generated rifampin-resistant mutants of Mycobacterium tuberculosis, we evaluated the performance of this test using 75 clinical isolates of Mycobacterium tuberculosis. With this small sample set, the TB-Biochip system displayed a sensitivity of 80% and a specificity of 100% relative to conventional drug susceptibility testing results for RIF resistance. For these samples (approximately 50% tested positive), the positive predictive value was 100% and the negative predictive value was 85%. Four of the seven observed discrepancies were attributed to rare and new mutations not represented in the microarray, while three of the strains with discrepant results did not carry mutations in the RIF resistance-determining region. The results of this study confirm the utility of the system for rapid detection of RIF resistance and suggest approaches to increasing its sensitivity.