Multicenter evaluation of reverse line blot assay for detection of drug resistance in Mycobacterium tuberculosis clinical isolates

A multicenter study was conducted with the objective to evaluate a reverse line blot (RLB) assay to detect resistance to rifampin (RIF), isoniazid (INH), streptomycin (STR), and ethambutol (EMB) in clinical isolates of Mycobacterium tuberculosis. Oligonucleotides specific for wild type and mutant (drug resistance linked) alleles of the selected codons in the genes rpoB, inhA, ahpC, rpsL, rrs, embB, were immobilized on a nylon membrane. The RLB assay conditions were optimized following analysis of DNA samples with known sequences of the targeted genes. For validation of the method at different geographical locations, the membranes were sent to seven laboratories in six countries representing the regions with high burdens of multudrug-resistant tuberculosis. The reproducibility of the assay for detection of rpoB genotypes was initially evaluated on a blinded set of twenty reference DNA samples with known allele types and overall concordant results were obtained. Further mutation analysis was performed by each laboratory on the local strains. Upon RLB analysis of 315 clinical isolates from different countries, 132 (85.2%) of 155 RIF-resistant and 28 (51.0%) of 55 EMB-resistant isolates were correctly identified, showing applicability of the assay when targeting the rpoB hot-spot region and embB306. Mutations in the inhA and ahpC promoter regions, conferring resistance to INH, were successfully identified in respectively 16.9% and 13.2% of INH-resistant strains. Likewise, mutations in rrs513 and rpsL88 that confer resistance to STR were identified in respectively 15.1% and 10.7% of STR-resistant strains. It should be mentioned that mutation analysis of the above targets usually requires rather costly DNA sequencing to which the proposed RLB assay presents rapid and inexpensive alternative. Furthermore, the proposed method requires the same simple equipment as that used for spoligotyping and permits simultaneous analysis of up to 40 samples. This technique is a first attempt to combine different targets in a single assay for prediction of antituberculosis drugs resistance. It is open to further development as it allows easy incorporation of new probes for detection of mutations in other genes associated with resistance to second-line (e.g., fluoroquinolones) and new antituberculosis compounds.