Phenotypic and genotypic drug sensitivity of Mycobacterium tuberculosis complex isolated from South Omo Zone, Southern Ethiopia

BACKGROUND: Knowledge of drug-sensitivity patterns of Mycobacterium tuberculosis complex (MTBC) strains isolated from patients is an important aspect of TB control strategy. This study was conducted to evaluate the drug sensitivity of MTBC isolates in South Omo, southern Ethiopia. MATERIALS AND METHODS: A total of 161 MTBC isolates (153 from new cases and eight re-treatment TB cases) were isolated using Lowenstein Jensen medium of which 126 isolates were able to be tested for drug sensitivity by BACTEC™MGIT™ 960 system, while all the 161 isolates were tested by GenoType(®) MTBDRplus VER 2.0. Descriptive statistics and logistic regression were used to express and present results. RESULTS: On the basis of MGIT 960 system, the prevalence of mono-resistance was 9.2% (11/119) in the new cases, although neither poly-resistance nor multidrug resistance (MDR) was recorded in these cases. On the basis of GenoType MTBDRplus assay, two of the 153 isolates (1.3%) of the new cases were mono-resistant for rifampicin (RIF) and one of these isolates had known rpoB gene mutation (H526D). One of the eight (12.5%) isolates obtained from the re-treatment cases was MDR with rpoB gene mutation (D516V) and katG gene mutation (S315T2). Taking MGIT 960 system as a gold standard, the sensitivities of the MTBDRplus assay were 33.3%, 100% and 100% for detection of resistance to isoniazid, RIF and MDR, respectively. On the other hand, its specificities were 99.2%, 100% and 100% for detection of resistance to RIF, isoniazid and MDR, respectively. CONCLUSION: The magnitude of drug resistance was relatively low in the new TB cases of South Omo as compared to the reports from the other regions of the country. This is encouraging and hence the TB Control Program in the Zone should strengthen its program so that the emergence of drug resistance is inhibited.