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Evaluation of the MB/BacT system for antimicrobial drug susceptibility testing of Mycobacterium tuberculosis

Abstract number: 903_r2347

Lago J.

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Objective:

Evaluate the ability of the MB/BacT culture system to perform antimicrobial susceptibility testing of Mycobacterium tuberculosis to isoniazid, rifampin, streptomycin and ethambutol by comparing the results to those obtained by the agar proportion method on Lowenstein-Jensen (LJ) medium.

Methods:

We performed paired antimicrobial susceptibility test (AST) on 34 Mycobacterium tuberculosis complex (Mt) clinical strains with the MB/BacT system (Biomérieux) using the BacT/ALERT SIRE kit and the agar proportion method on LJ using the Mycobacterial susceptibility testing (Biomérieux). The control strain H37Rv (ATCC 27294) was tested by both methods as a quality control. All strains were identified by the Accuprobe culture identification test (Gen Probe). Four antimicrobial drugs were evaluated: streptomycin (1.0 mg/mL in MB/BacT and 4.0 and 10.0 mg/mL in LJ), isoniazid (0.1 mg/mL in MB/BacT and 0.2 and 1.0 mg/mL in LJ), ethambutol (5.0 mg/mL in MB/BacT and 2.0 and 3.0 mg/mL in LJ) and rifampin (1.0 mg/mL in MB/BacT and 20 and 40 mg/mL in LJ). The tests were conducted according to the instructions given by the manufacturer.

Results:

The control strain H37Rv performed as expected: susceptible to four drugs by the two methods. Of the 34 Mt strains tested with the MB/BacT system, we detected seven strains resistant to one or more drugs (three were multiresistants) and 27 strains susceptible to all four drugs. Full agreement of rifampin and isoniazid results was found for all isolates. The two methods showed concordance for the four drugs tested in 30 strains (88.2%). There was disagreement in one case (2.9%) for Ethambutol (resistant by LJ and susceptible by MB/BacT) and three cases (8.8%) for streptomycin (one susceptible by LJ and resistant by MB/BacT and two resistants by LJ and susceptibles by MB/BacT). Turnaround times for AST ranged from 5.5 to 13.0 days for MB/BacT.

Conclusions:

These results indicate that the MB/BacT system is shown to be a reliable, rapid, fully automated, nonradiometric system for the susceptibility test of Mycobacterium tuberculosis complex.

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Session Details

Date: 01/08/2007
Time: 00:00-00:00
Session name: XXIst ISTH Congress
Subject:
Location: Oxford, UK
Presentation type:
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