Abstract:

Objective: To evaluate the effect of a new domestic improved Middlebrook liquid culture reagent on the culture of Mycobacterium tuberculosis in clinical. Methods: Sputum and alveolar lavage fluid samples of suspected pulmonary tuberculosis patients diagnosed and treated in Xi’an Chest Hospital from March to April 2021 were collected. Eighty-nine sputum samples and 61 alveolar lavage fluid samples were qualified and cultured with mycobacterium modified reagent and BACTEC MGIT 960 (MGIT 960). The positive rate, positive reporting time and contamination rate of mycobacterium detection by the two methods were compared, and the detection efficiency of the improved reagent method was evaluated refered to the culture results of MGIT 960. Results: The total positive rate and positive reporting time (median (quartile)) of sputum and alveolar lavage fluid samples detected by mycobacterium modified reagent method were not significantly different from the culture results of MGIT 960 ((44.7% (67/150) vs. 42.7% (63/150), χ²=0.571, P=0.453; 13.0 (8.5, 17.0) d vs. 13.0 (8.0, 17.5) d, Z=-1.344, P=0.179). There was no contamination in alveolar lavage fluid samples detected by the two methods, but the contamination rate of sputum samples detected by the improved reagent method (12.4% (11/89)) was significantly higher than that of MGIT 960 culture (4.5% (4/89))(χ²=4.000,P=0.039). The cost of the improved culture reagent (RMB (49.6±10.5) yuan/person) was only about 60% of that of MGIT 960 culture reagent (RMB (75.4±15.8) yuan/person). Using MGIT 960 culture results as the standard, the total sensitivity and specificity of the improved reagent method for sputum and alveolar lavage fluid samples were 96.9% (62/64) and 94.2% (81/86), the Kappa value was 0.905, showing excellent consistency. Conclusion: Mycobacterium modified Middlebrook liquid culture reagent has the good consistency of MGIT 960 culture in the detection of sputum and alveolar lavage fluid, however, attention should be paid to the high contamination rate of sputum specimens.

Key words: Mycobacterium tuberculosis, Culture techniques, Diagnostic self evaluation, Comparative study