Background: Performance of Genotype MTBDRplus assay against Lowenstein Jensen (LJ)
proportion method of Drug Susceptibility Testing (DST) in detection of resistance among clinical
mycobacteria isolates to rifampicin (RMP) and isoniazid (INH) was evaluated in Ilorin, Nigeria.
Methods: This retrospective study characterized one hundred mycobacteria isolates from pulmonary
TB patients, stored on LJ medium and subcultured unto fresh LJ slants before being genotyped using
MTBDRplus assay. DST was performed on the isolates against RMP, INH, Ethambutol and Streptomycin.
Results: Genotype MTBDRplus identified 97% and 3% of the 100 isolates as Mycobacterium tuberculosis Complex
(MTBC) and Non-Tuberculous Mycobacteria (NTM) respectively. Fourteen of the isolates, (14%) were resistant to RMP
while 86% were sensitive by the genotypic method. Three of these 14 RMP-resistant isolates were NTMs while 11 were
MTBC. Twelve (12%) of the 100 isolates were resistant to INH. Three INH-resistant isolates were NTMs, and 9 were
MTBC. Phenotypically and genotypically, the 3 NTMs were resistant to RMP and INH and ten of the 97 MTBC strains
were RMP-resistant. One RMP-phenotypically-sensitive strain was genotypically resistant to RMP. Six of the MTBC
isolates were resistant to both RMP and INH by both methods. Most mutations occurred in the S-531L and S315T1
codons of rpoB and KatG genes of RMP and INH, respectively.
Conclusion: The high specificity and positive predictive values recorded by MTBDRplus in our study make it suitable for
use in the programmatic management of drug-resistant TB in resource-limited settings.