Antimicrobial susceptibility rates of Mycobacterium tuberculosis against first-line drugs

Abstract number: r2218

Azap  Ö.K., Arslan  H., Timurkaynak  F., Oruç  E., Togan  T., Yapar  G.

Objectives: 

Mycobacterium tuberculosis infects one third of the world's population. Culture is the "gold standard" for detecting mycobacteria in clinical specimens. Testing of M. tuberculosis isolates for drug susceptibility is important to guide therapy. The aim of this study is to report the antibacterial susceptibility rates of M. tuberculosis strains isolated in our laboratory.

Methods: 

Laboratory records between January 2001 and January 2005 were evaluated retrospectively. Susceptibility rates against first line drugs (Isoniazid (INH), rifampin (RMP), ethambutol (EMB), streptomycin (STM)) were recorded. Lowenstein-Jensen agar and BACTEC 460 TB system were used for culture. Acid-fast stain was performed for each sample.

Results: 

A total of 5602 materials (2104 respiratory specimen, 1275 urine, 788 body fluids, 445 tissue specimen, 990 others) were admitted to the laboratory for acid-fast stain and mycobacterium culture. M. tuberculosis was detected by culture in 145 (2.5%) of 5602 samples. Acid-fast stain was positive in 46 (31.7%) of 145 samples. Growth was detected only in BACTEC 460 TB but not in Lowenstein Jensen agar for 16 (11%) of the 145 samples. Seven of these 16 samples were pus and the others were, bronchoalveolar lavage fluid and tissue specimen. The results of acid-fast stain were also negative for these 16 samples. One hundred and fifteen (79.3%) of 145 M. tuberculosis strains were sensitive to all four antibiotics (INH, RMP, EMB, STM) tested. Sixteen (11%) were resistant to only INH, 3 (2%) were resistant to only RMP, 3 (2%) were resistant to both INH and RMP, 3 (2%) were resistant to INH and EMB, 2 (1.3%) were resistant to INH, RMP and STM and 3 (2%) were resistant to all 4 antibiotics tested.

Conclusion: 

1. Eleven percent of the positive culture result were obtained only by BACTEC 460 TB system, this demonstrates that BACTEC 460 TB is superior to conventional methods (Lowenstein Jensen agar and acid fast stain) in the detection of M. tuberculosis.

2. As approximately 20% of M. tuberculosis strains are resistant to at least one first line antibiotic, treatment of tuberculosis should be guided by antimicrobial susceptibility results in our country.