Correlation Between Xpert MTB/RIF Results and rpoB Mutations within Probe-Targeted Regions in Mycobacterium tuberculosis Isolates from Sichuan Basin.

Purpose: 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.