EVALUATION OF THE GENOTYPE MTBDR ASSAY FOR RAPID DETECTION OF RIFAMPIN AND ISONIAZID RESISTANCE IN CLINICAL MYCOBACTERIUM TUBERCULOSIS COMPLEX CLINICAL ISOLATES

Rapid identification of resistant Mycobacterium tuberculosis complex isolates is quite important for the establishment of early and appropriate therapy. The Genotype MTBDR (Hain Lifescience, Nehren, Germany) is a commercially available DNA strip assay designed for the rapid detection of rpoB and katG gene mutations in clinical isolates. This study was conducted to determine the mutation types of phenotypically drug resistant 26 M.tuberculosis complex clinical isolates [15 isoniazid (INH), 1 rifampin (RMP) and 10 INH and RMP resistant] by Genotype MTBDR (G-MTBDR) DNA strip assay and to compare the diagnostic performance of this test. Sixteen of 25 (64%) INH-resistant and 9 of 11 (81.8%) RMP-resistant clinical isolates were correctly identified with the presence of hybridization in mutation probe or lack of hybridization at least by one of the wild type probes, by G-MTBDR assay. Hybridization with mutation probes was detected in only 5 of the RMP resistant isolates. We observed rpoB MUT3 (S531L, Ser -> Leu) mutation in 4 and rpoB MUT1 (D516V) in one of these isolates. In 56% (14/25) of the INH-resistant isolates, katG T1 (S315T1) hybridization pattern was observed at katG mutation probe. G-MTBDR assay couldn't identify two of the 11 (18.2%) RMP-resistant isolates and one of these isolates was shown to have a mutation at codon 531 (TCG -> GCG) and the other at codon 545 (CTG->ATG), possibly not associated with resistance, by sequence analysis. In four of the eight (8/25; 32%) INH-resistant isolates not identified by G-MTBDR assay, DNA cycle sequencing revealed different nucleotide changes outside the most common mutation zone. One of these were at codon 293 (GCT -> ACT) in katG, one with dual mutation at 279 (GGC -> ACC) in katG and at 15(th) C -> T in inhA gene, one at 15(th) C -> T in inhA gene and one at 279 (GGC -> ACC) in katG gene region. DNA membrane strip assay can be a useful tool for the rapid detection of resistant M.tuberculosis complex isolates and therefore accelerate the initiation of the appropriate treatment. However, due to its restrictions in the determination of relatively rare mutations, this rapid screening test should be used together with conventional susceptibility tests in routine laboratory practices.