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

Objective: to assess the efficacy of a line-probe assay ä (lipa) as rapid diagnostic test for early detection of drug-resistant tuberculosis compared to conventional susceptibility methods in pakistan. methods: 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. results: 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. conclusion: 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.