| Summary: | Kun Li,&ast; Long Li&ast; Department of Clinical Laboratory Medicine, Suining Central Hospital, Suining, Sichuan, People’s Republic of China&ast;These authors contributed equally to this workCorrespondence: Kun Li, Department of Clinical Laboratory Medicine, Suining Central Hospital, Suining, Sichuan, People’s Republic of China, Tel +86-136-9835-569, Email 286483463@qq.comPurpose: This study characterized mutation patterns within the rifampicin resistance-determining region (RRDR) of the rpoBgene (codons 507– 533), targeted by Xpert MTB/RIF probes, in Mycobacterium tuberculosis isolates from Southwest China. Regional molecular profiles were and compared regional profiles against global datasets to elucidate implications for rifampicin resistance surveillance.Methods: We conducted a retrospective study of 197 rifampicin-resistant tuberculosis cases involving 197 cases of rifampicin-resistant tuberculosis (comprising 194 pulmonary and 3 extrapulmonary cases) confirmed through the GeneXpert MTB/RIF assay at Suining Central Hospital during 2023– 2024. Mutation characteristics across five RRDR probes (labeled A–E) were assessed, along with the semi-quantitative classification of bacterial loads.Results: Single-probe mutations predominated (82.7%; 163/197), with hotspots at Probe E (S531L, 55.8%) and Probe A (Q510H/V511D, 12.2%). Dual-probe mutations (16.8%, 33/197) were primarily A+B combinations (13.7%, 27/197), showing significantly elevated prevalence in patients aged 46– 60 years (OR = 2.31, 95% CI: 1.12– 4.79, P< 0.05). Bacterial load stratification revealed strong diagnostic accuracy associations: smear positivity rates were 79.4% (high load) and 44.4% (medium), while culture positivity rates were 67.6% and 57.8%, respectively.Conclusion: A unique double-peak mutation pattern (primarily involving probes E and A) was identified in Sichuan Province, which contrasts sharply with the single hotspot pattern observed in Europe and the epidemiological pattern in Beijing, China, where probe E predominates. The elevated Probe A mutation rate (12.2%) potentially reflects regional rifabutin usage in second-line regimens. These findings provide molecular epidemiological insights for optimizing diagnosis and drug resistance monitoring in southwestern China.Keywords: Mycobacterium tuberculosis, rpoB gene, drug resistance
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