Abstract:

Objective This study aimed to analyze the application value of culture-positive bacterial samples with the BACTEC MGIT 960 system (referred as “MGIT 960 system ”) prepared by sonication nephelometer method for the drug sensitivity test (DST) of mycobacteria. Methods A total of 1086 culture-positive mycobacteria samples detected by MGIT 960 system were collected in Xi’an Chest Hospital from January to December 2018. Among these samples, 818 bacterial samples underwent DST using MGIT 960 system, including 100 samples treated by MGIT 960 system recommended method and 718 samples treated by sonication nephelometer; and 268 bacterial samples conducted DST with the proportional method, including 30 samples treated by the traditional grinding method and 238 samples treated by the sonication nephelometer. The values of the bacterial samples treated by sonication nephelometer for DST detected by MGIT 960 system and the proportional method were compared with traditional bacterial samples. Results The results of DST using the MGIT 960 system for 0.6-1.0 McFarland standards samples treated by the sonication nephelometer were mainly reported on 8-10 days. The bacterial samples treated by the MGIT 960 system were evenly reported on 5-14 days. The reporting rates of the system X200 (small amount of live bacteria) of 0.6, 0.7, 0.8, 0.9, 1.0 McFarland standards samples by sonication nephelometer treatment method (0.00%, 0.00%, 0.00%, 0.72% (1/138), 1.31% (2/153), respectively) were lower than that treated by MGIT 960 method (11.00%, 11/100), with the statistically significant differences (χ ²=11.41, 9.94, 12.43, 12.79, 11.28, all P<0.01). When the second-line DST with the proportional method was carried out, the bacterial sample treated by sonication nephelometer basically reached the target turbidity after 6 to 7 days of enrichment, while the bacterial sample treated by traditional grinding method only reached 80% of the target turbidity on the 7th day of enrichment. The bacterial samples with the turbidity of 0.7, 0.8, 0.9, and 1.0 McFarland standards was treated by sonication nephelometer, and the success rate of DST was 82.61% (19/23), 82.69% (43/52), and 94.00% (47/50), 96.00% (48/50), respectively, which was similar to the success rate of the DST of the bacterial samples treated by the traditional grinding method (83.33%, 25/30), without the statistically significant differences (χ ²=0.01, 0.01, 2.37, 3.77, all P>0.05). Conclusion The MGIT 960 culture-positive bacterial samples that treated by sonication nephelometer can improve the success rate of DST by MGIT 960 system, and shorten the detection time of DST with the proportional method.

Key words: Mycobacterium tuberculosis, Sonication, Nephelometry and turbidimetry, Specimen handling, Microbial sensitivity tests, Comparative study