[Rapid diagnosis and susceptibility of Mycobacterium tuberculosis to antibiotics using MGIT system]

New technologies for rapid detection and drug susceptibility testing of mycobacteria are needed in clinical laboratories in order to attempt a rapid diagnosis and effective treatment of tuberculosis (TB) specially of cases resistant to isoniazid (H) and rifampin (RMP) (MDR-TB). A total of 218 pulmonary specimens from 132 HIV coinfected patients were processed and inoculated into the Mycobacterial Growth Indicator Tube system (MGIT, Becton Dickinson, MD) and on Lowenstein-Jensen (L-J) and Stonebrink (SB) solid media. The average time for recovering Mycobacterium tuberculosis (MTB) from MGIT was 18.3 days and 31.0 days from solid media. Of the patients 14.4% (19/132) were only diagnosed by MGIT. In another experiment susceptibility tests by the classical proportion method (PM) in L-J medium with H, RMP, streptomycin (SM), para-aminosalycilic-acid and ethambutol (EMB) were carried out on 120 isolates. The results were later compared with those obtained by determining the minimal inhibitory concentration (MIC) for each drug in MGIT against the above mentioned isolates. MIC results from MGIT method were available in an average of 5 days (3-10) and they correlated (correlation index 0.9974) with those of drug susceptibility obtained by the PM. A 4.7% (2/42) of disagreement among detecting isolates resistant to H and SM was found between PM and MGIT. Our results showed MGIT as a useful, safe and timesaving culture system, specially for detecting TB resistance. It might be used in clinical laboratories to improve the proper management of TB patients.