Abstract:

Objective: To analyze the mutation distribution and frequency of RNA polymerase β subunit (rpoB) gene probe in tuberculosis (TB) patients with GeneXpert MTB/RIF (Xpert) positive rpoB gene mutation, and to elucidate the mutation characteristics of rifampicin resistance determining region. Methods: A total of 682 consecutive TB patients with positive Xpert test and rpoB gene mutation who visited Beijing Chest Hospital, Capital Medical University from June 2019 to June 2020 were involved, including 618 pulmonary TB (PTB) cases and 64 extrapulmonary TB (EPTB) cases. Clinical examination samples, including 465 sputum, 153 bronchoalveolar lavage fluid, 37 pus, 19 pleural effusion, 7 stool and 1 cerebrospinal fluid, were collected from patients. All Xpert positive specimens were analyzed for semi-quantitative results of Mycobacterium tuberculosis (MTB) and mutation distribution of the rpoB gene probe. Results: Of the 682 samples, 6.45% (44/682) were high, 25.07% (171/682) were medium, 25.51% (174/682) were low, and 42.96% (293/682) were very low in MTB semi-quantitative. The proportion of very low levels of MTB semi-quantitative was significantly higher in EPTB samples than in PTB samples (64.06% (41/64) vs. 40.78% (252/618), χ ²=12.83, P<0.001). Smear positive rates were 84.62% (33/39), 64.02% (105/164), 27.27% (42/154), and 7.84% (20/255) in semiquantitatively high, medium, low, and very low levels of MTB specimens, respectively. The mutation rate of the rpoB gene was 92.82% (633/682) for single probe, 6.89% (47/682) for double probe, and 0.29% (2/682) for triple probe. The mutation rate of probe E was the highest in specimens with single probe mutation (74.34%, 507/682), followed by probe D (8.80%, 60/682); the mutation rate of probe D+E was the highest in specimens with double probe mutation (4.25%, 29/682), followed by probe A+B (1.76%, 12/682); and all three probe mutations were probe A+D+E (2 cases). Conclusion: Single probe mutation is predominant in Xpert positive rpoB gene mutation MTB, and the most common mutation probes in PTB and EPTB are probe E and probe D.

Key words: Mycobacterium tuberculosis, Nucleic acid amplification techniques, Genes,bacterial, Mutation, Nucleic acid probes