Genotypic assessment of drug-resistant tuberculosis in Baghdad and other Iraqi provinces using low-cost and low-density DNA microarrays

Abstract

We report on a molecular investigation carried out to ascertain the prevalence of drug-resistant tuberculosis (TB) and the specific gene mutations responsible for resistance to rifampicin (RIF) and/or isoniazid (INH) in Iraq. In total, 110 clinical isolates from category II TB cases from Baghdad (58 %) and several Iraqi provinces (42 %) were analysed using colorimetric, low-cost and low-density (LCD) microarrays (MYCO-Direct and MYCO-Resist LCD array kits) to identify the point mutations responsible for resistance in Mycobacterium tuberculosis isolates. We found 76 patients (69.1 %) had resistant strains, of which 40 (36 %) were multidrugresistant (MDR)-TB. Where mono-resistance was identified, it was found to be predominantly to RIF (83 %). The most common mutations were rpoB S531L (50 %), inhA C15T (25 %) and katG S315T (15 %). The most common MDR-TB genotypes were rpoB S531L with inhA C15T (60 %) and rpoB S531L with katG S315T (20 %). Where phenotypic analysis of clinical isolates was also performed, genotypic data were found to show excellent correlation with phenotypic results. Correlation was found between the MYCO-Resist LCD array and GenoType MTBDRplus for detection of resistance to RIF. Our study shows MDR-TB in 36 % of category II TB cases in Baghdad and surrounding Iraqi provinces, which reflects the World Health Organization findings based on phenotypic studies. Diagnosis of TB and MDR-TB using culture-based tests is a significant impediment to global TB control. The LCD arrays investigated herein are easy to use, sensitive and specific molecular tools for TB resistance profiling in resource-limited laboratory settings.

Use of DNA microarray chips for the rapid detection of Mycobacterium tuberculosis resistance to rifampicin and isoniazid

“…The technique has been used widely for multiple applications due to its rapidness, accuracy, high efficiency and easy operation (20). For different mutations, the corresponding oligonucleotide probes are designed and immobilized on a solid support.…”

“…Briefly, the DNA microarray chip technique (20) was used to test mutations in the rpoB gene at the 511, 513, 526, 531 and 533 codons (common mutation sites) to give an indication of RFP resistance in the RRDR. For INH resistance, the katG315 and inhA-15 mutation sites were assessed.…”