Line probe assay for detection of rifampicin and isoniazid resistant tuberculosis in Pakistan

To assess the efficacy of a line-probe assay delta (LiPA) as rapid diagnostic test for early detection of drug-resistant tuberculosis compared to conventional susceptibility methods in Pakistan. Resistance to rifampicin (RIF) and isoniazid (INH) in 108 smear-positive pulmonary tuberculosis samples was detected using a line-probe assay [GenoType MTBDRplus (Hain Lifescience, GmbH, Nehren, Germany)] at the clinical microbiology laboratory of Aga Khan University Hospital in May, 2009. Results were compared with susceptibilities performed while using agar proportion. In comparison to the agar proportion method, the detection rate and specificity of resistance using MTBDR plus was 92.5% and 98.2% for rifampicin, and 76.3% and 100% for isoniazid. Mutations in codons 531 and 533 of rpoB gene (62%S531L) were responsible for 67.9% of rifampicin resistance. S315T mutation of katG gene was detected in 55.9% and inhA promoter mutation at positions -15 (C15T) in 11.9% of isoniazid resistant isolates. Four phenotypically rifampicin-resistant and 14 isoniazid-resistant strains were not detected by MTBDRplus. Sequencing these strains revealed mutations in 4 strains; 2 in rpoB gene S531W, del518 and 2 in katG genesW300L, S315N. Hence, two phenotypic rifampicin-resistant and 13 phenotypic isoniazid-resistant strains were not detected by the commercial line probe assay. The study showed that MTBDRplus had a high detection rate for rifampicin resistance. However, additional probes need to be included in the assay to improve the detection of isoniazid-resistant mycobacterium tuberculosis strains in Pakistan.