Evaluation of the BACT/ALERT 3D system for testing susceptibility of Mycobacterium tuberculosis to first-line antituberculosis agents: comparison with BacTec MGIT 960 and Lowenstein-Jensen proportion method

Abstract number: 1733_1138

Guney C., Suel A., Karagoz T., Yorulmaz Y.

Objectives: The performance of the BACTALERT 3D (BTA) system for the testing of Mycobacterium tuberculosis susceptibility to streptomycin (STR), isoniazid (INH), rifampin (RIF) and ethambutol (ETH) was evaluated with 101 clinical isolates and compared with BACTEC MGIT 960 (M960) system and Lowenstein-Jensen (L-J) proportion method (currently used) from clinical specimens at Sureyyapasa Chest Disease Hospital.

Methods: A series of different samples recovered from patients in hospital were cultivated in three systems at the same time according to NaOH %3+NALC decontamination protocol. BTA and M960 susceptibility testing was performed as described by instructions of manufacturers. M. tuberculosis H37Rv (ATCC 27294) standard strain was used for quality control of the all tests.

Results: In all, there were 404 test combinations with a total of 19 discrepancies (4.7%) between M960 and BTA results. Total agreements were 95.3%. The discrepancies resolved in favour of the M960 system in 11 cases and in favour of the BTA system in 8 cases according to L-J proportion method. The BTA system produced 3 very major errors (VME) and 8 major errors (ME), while the M960 showed 2 VME and 6 ME. No statistically significant differences were found. The mean times of detection for BTA and M960 were 16.3 days and 12.2 days, respectively. Two smear negative sputums detected by BTA in 26 and 36 days were not detected by M960. Turnaround times from detection to reporting SIRE results for BTA and M960 were 12.8 and 11.4 days, respectively. No statistically significant differences were found. The contamination rate for BTA, MGIT and L-J were 2%, 4%, 3% respectively.

Conclusion: Some discordant results between the standard test and the test method could be attributed to the presence of borderline-resistant strains, mainly in relation to LJ tests where the final results depend on an accurate count of colonies. These results suggest that BACTALERT 3D system is a valid alternative to the BACTEC MGIT 960 for M. tuberculosis susceptibility testing.

Session Details

Date: 31/03/2007
Time: 00:00-00:00
Session name: European Society of Clinical Microbiology and Infectious Diseases
Location: ICC, Munich, Germany
Presentation type:
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