Comparative evaluation of bactec 460tb system and lowenstein-jensen medium for the isolation of M. tuberculosis from cerebrospinal fluid samples of tuberculous meningitis patients

Purpose : To evaluate the role of the radiometric BACTEC 460TB system and the conventional Lowenstein-Jensen (LJ) medium for isolation of M. tuberculosis from cerebrospinal fluid (CSF) samples of tuberculous meningitis (TBM) patients. Methods : CSF specimens (n=2325) from suspected TBM patients were processed for isolation of mycobacteria by inoculating BACTEC 12B medium and the LJ medium. The isolation of mycobacteria in both media was confirmed by microscopy and biochemical identification. Drug sensitivity testing for the anti-TB drugs was carried out by BACTEC radiometric method. Results : Among the total 2325 CSF specimens processed by both methods, M. tuberculosis was isolated from 256 specimens. The isolation rates were 93% and 39% for the BACTEC system and LJ medium respectively. Both the media supported growth in 32% of the culture-positive specimens. BACTEC system alone yielded growth in 61% and LJ alone in 7%, of the culture-positive specimens. Among 205 isolates tested for drug susceptibility 81% were sensitive to all the drugs tested and 19% were resistant. Conclusions : The BACTEC 460TB system provides a highly sensitive and rapid tool for the isolation and drug susceptibility testing of M. tuberculosis , from CSF of TBM patients. Use of a solid medium in conjunction with the BACTEC 12B medium is essential for optimal recovery for M. tuberculosis from CSF specimens.

Keywords
BACTEC radiometric method, cerebrospinal fluid, Lowenstein-Jensen medium, sensitivity, tuberculous memingitis