Background: Drug-Resistant Tuberculosis (DR-TB) is one of the major public health issues globally. Zambia is highly burdened by TB and multi-drug resistant TB. In this study, sputum samples obtained from the new and previously treated cases of TB were examined for drug-resistant Mycobacterium tuberculosis (MTB). Methods: Sputum specimens were processed using the N-acetyl-L-cysteine-sodium hydroxide method, stained and examined using fluorescent technique and microscopy respectively. Mycobacterial DNA was extracted using the Genolyse kit, then subjected to multiplex polymerase chain reaction amplification and reverse hybridization. Drug-resistance and mutations in MTB genes were detected using the Genotype MTBDRplus VER 2.0 and MTBDRsl VER 2.0 assays. Results: A total of 329 MTB-positive sputum specimens, 102 from the new TB cases and 227 from previously treated TB cases, were analysed for drug-resistance. Among the new TB cases, 3.9% had Rifampicin (RIF) mono-resistance, 12.8% Isoniazid (INH) mono-resistance, and 17.7% had Multi-Drug Resistance (MDR). For the previously treated TB cases, 10.1% had RIF mono-resistance, 6.6% INH mono-resistance, 33.0% MDR, 1.8% poly-drug resistance, and 0.8% had pre-Extensively Drug-Resistance (pre-XDR). Mutations identified were rpoB (Ser531Leu, His526Asp, Asp516Val, His526Tyr, and Glu510His), katG (Ser315Thr 1 and Ser315Thr 2), InhA (Cys15Thr), gyrA (Ala90Val and Asp94Gly), and eis (Cys14Thr), each with a varying frequency. Conclusion: DR-TB is prevalent, especially MDR-TB, which is currently the most worrisome form of DR-TB and an emerging threat hampering efforts in the control of TB in Zambia. The early detection and effective treatment of TB cases are key in the control of DR-TB.

Drug-Resistant Tuberculosis (DR-TB) causes high mortality and morbidity rates globally. DR-TB and COVID-19 pandemic are posing a major risk to global public health and economic security, and are jeopardizing efforts in the control, prevention and elimination of TB globally. Mycobacterium tuberculosis (MTB) has continued to evolve resistance to anti-TB drugs. Different types of DR-TB have been defined and they include; mono drug-resistant TB, Multi Drug-Resistant TB (MDR-TB), poly drug-resistant TB, pre-Extensively Drug-Resistant TB (pre-XDR TB), Extensively Drug-Resistant TB (XDR-TB), Extremely Drug-Resistant TB (XXDR-TB), and Totally Drug-Resistant TB (TDR-TB). DR-TB is caused by several factors which include: non-adherence, poor compliance, low efficacy anti-TB drugs, delayed diagnosis, interrupted supply, stock-outs, inadequate infection control, HIV co-infection, spontaneous mutations, and chromosomal replication errors. Global TB targets have gone off-track and years of progress reversed due to DR-TB and the COVID-19 pandemic. Treatment failure, death and costs incurred are higher among patients suffering from DR-TB than among those with susceptible TB. For this reason, susceptible TB needs to be diagnosed quickly and treated effectively to prevent its progression to DR-TB. Treatment for susceptible TB requires the use of first-line anti-TB drugs; rifampicin, isoniazid, pyrazinamide, and ethambutol. While DR-TB is treated using the second- and third-line anti-TB drugs. Effective treatment of TB is dependent on: prompt and accurate diagnosis of TB and recognition of drug-resistance; adherence to treatment; robust contact tracing and prophylactic treatment of TB contacts; and screening for TB infection in high-risk groups.

Drug-resistant tuberculosis is a threat to the control of tuberculosis globally, it develops mainly due to mutations in target genes of (MTB). Mutations in the rpoB gene confer resistance to rifampicin (RIF). The most frequent mutations conferring resistance to RIF include; Ser531Leu, Asp516Val, and His526Asp. Isoniazid resistance (INHr) occur most frequently due to mutations in the and its promoter. Most frequent mutation in is Ser315Thr 1, while in inhA include; Thr8Cys, Ala16Gly, and Cys15Thr. Mutations in , and genes confer resistance to ethambutol. 70% of mutations in the gene occur in codon 306, 406, or 497 and include; Met306Leu, Gly43Cys, and Ser412Pro. Mutations in the , and genes mediate resistance to pyrazinamide. Frequent mutations in A include; Tyr64Ser, Phe94Ala, and Trp68Gly. MTB resistance to streptomycin (STR) occur due to mutations in the , B, and L genes. Mutations (Ala80Pro), and L (Lys43Arg) confer resistance to STR. Fluoroquinolone resistance is mediated via mutations in the A and B genes. The most common mutations in the A gene include; Gly88Cys, Ala90Val, and Ser91Pro. While those in the gyrB gene include; Glu540Val, and Asn538Asp. Mutations in the rrs and promoter region cause resistance to the kanamycin and amikacin. While mutations in the and A cause resistance to capreomycin and viomycin. Common mutations in include; Cys1402Thr, Ala1401Gly, and Gly1484Thr. While mutations in the include; Cys12Thr, Gly10Ala, and Gly37Thr.Detection of drug-target genes and their mutations has therapeutic and diagnostic value.