Performance comparison of four methods for detecting multidrug-resistant Mycobacterium tuberculosis strains

National Tuberculosis Reference Laboratory, Kuwait.

To compare Genotype MTBDRplus (gMTBDR(+)), INNO-LiPA Rif.TB (INNO-LiPA), polymerase chain reaction-restriction fragment length polymorphism (PCR-RFLP) and DNA sequencing for detecting rifampicin (RMP) and/or isoniazid (INH) resistance-associated mutations in the rpoB hot-spot region (HSR-rpoB), the katG codon 315 (katG315) and the inhA regulatory region (inhA-RR) among multidrug-resistant Mycobacterium tuberculosis (MDR-TB) isolates.

A total of 82 MDR-TB and 43 pansusceptible M.tuberculosis BACTEC 460-characterised isolates were processed using molecular techniques and the Mycobacterial Growth Indicator Tube (MGIT) 960 system.

All susceptible strains contained wild-type sequences in target genes. RMP resistance was detected in respectively 78, 77 and 79 MDR-TB strains by gMTBDR(+), INNO-LiPA and HSR-rpoB sequencing. Two isolates with Ins514TTC mutation were detected as RMP-resistant by gMTBDR(+) but as RMP-susceptible by INNO-LiPA. One isolate with L533P mutation, detected as RMP-susceptible by gMTBDR(+), was detected as RMP-resistant by INNO-LiPA. Two of three isolates detected as RMP-susceptible by gMTBDR(+), INNO-LiPA, HSR-rpoB sequencing and the MGIT 960 system contained a I572F mutation that is outside HSR-rpoB. INH resistance was detected in respectively 76, 60, 60 and 22 MDR-TB strains by gMTBDR(+), katG315 PCR-RFLP, katG315 sequencing and inhA-RR sequencing.

Although gMTBDR(+) accurately detected ∼ 88% of MDR-TB strains, some rpoB mutations were either missed or were outside the region of analysis of the gMTBDR(+) assay.