Resistance Reversal Activity of Phytochemicals from Zanthoxylum zanthoxyloides Against Multidrug-Resistant Mycobacterium tuberculosis in North East Nigeria

Multidrug-resistant tuberculosis (MDR-TB) presents a catastrophic public health threat in North East Nigeria, where conflict, displacement, and collapsed health infrastructure in Borno, Yobe, and Adamawa States have created conditions of extreme TB vulnerability. The urgent need for novel anti-TB agents and adjuvant resistance reversal strategies has renewed interest in bioactive plant compounds targeting mycobacterial drug resistance mechanisms. Zanthoxylum zanthoxyloides, distributed across the savannah zones of Nigeria, contains alkaloids and terpenoids with reported antimycobacterial properties. This study investigates the resistance reversal activity of fractionated Zanthoxylum zanthoxyloides bark extracts against clinical MDR-TB Mycobacterium tuberculosis isolates obtained from patients at the Federal Neuropsychiatric Hospital TB Unit, Maiduguri. MDR-TB isolates were characterised by GeneXpert MTB/RIF and phenotypic drug susceptibility testing. Minimum bactericidal concentration (MBC) against drug-susceptible and MDR strains was determined. Resistance reversal potential was evaluated by combining plant fractions with isoniazid and rifampicin at sub-therapeutic concentrations in checkerboard assays, with fractional inhibitory concentration index (FICI) determination. Efflux pump inhibition was assessed by ethidium bromide cartwheel assay and real-time PCR of efflux genes (mmr, rv1258c). Two alkaloid-enriched fractions reduced MBC of rifampicin against MDR isolates by 4-16-fold. Efflux pump activity was significantly inhibited. Novel fagaronine analogue characterised by 2D-NMR demonstrated MBC of 2.1 ug/mL against MDR strains. This study identifies phytochemical efflux pump inhibitors as viable resistance reversal candidates for MDR-TB adjunctive therapy. Keywords: MDR-TB, Zanthoxylum zanthoxyloides, resistance reversal, efflux pump, North East Nigeria