Mechanistic Investigation of Mycobacterium tuberculosis Drug Efflux Pump Overexpression in MDR-TB Strains Circulating in North West Nigerian Communities

Drug efflux pump overexpression constitutes a significant but undercharacterised contributor to the multidrug-resistant tuberculosis (MDR-TB) phenotype, providing resistance independent of canonical katG and rpoB mutations, yet this mechanism has never been systematically investigated in MDR-TB strains circulating in North West Nigeria. This dissertation mechanistically investigates efflux pump contribution to MDR-TB resistance in Mycobacterium tuberculosis strains from patients in Kano, Kebbi, and Zamfara States, North West Nigeria. Fifty MDR-TB isolates confirmed by GeneXpert and confirmed susceptibility testing (DST) were selected, including 20 with classical katG/rpoB mutations and 30 phenotypically resistant but mutation-negative. Efflux pump gene expression (mmpL5, Rv1258c, efpA, Rv2936) was quantified by RT-qPCR. Efflux pump inhibitor (EPI) assays using carbonyl cyanide m-chlorophenylhydrazone (CCCP) and piperine assessed contribution of pumps to drug MIC. Whole genome sequencing characterised regulatory mutation landscapes. Efflux pump overexpression contributed to resistance in 43 percent of phenotypically resistant strains lacking classical mutations. mmpL5 and Rv1258c were the most overexpressed pumps. EPI treatment reduced isoniazid and rifampicin MICs by 4 to 8-fold in 68 percent of pump-overexpressing strains, confirming efflux as a major resistance mechanism. Regulatory mutations in Rv0678 and whiB7 promoters were identified as novel drivers of pump overexpression. The dissertation advances MDR-TB resistance mechanism understanding with relevance to North West Nigerian TB control and EPI-combined therapy development. Keywords: MDR-TB, efflux pumps, Mycobacterium tuberculosis, North West Nigeria, drug resistance mechanism