Assessment of a biphasic culture system for mycobacteria isolation from patients highly suspected of tuberculosis.
The efficiency of a biphasic culture medium, MB-Check (MB) for mycobacterial isolation was assessed versus two egg-based media: Loewenstein-Jensen and Coletsos (LJC). 74 specimens from 30 patients highly suspected of tuberculosis were inoculated on all three media. Smear examination gave 20 positive samples out of 74 (presence of acid-fast bacilli: AFB). All these specimens gave a positive culture on the MB medium. However, 20% of the samples did not grow on LJC, mainly due to contaminants (non-significant difference, p > 0.05). 32 samples out of 74 were found positive for Mycobacterium tuberculosis with MB-Check, and 25 out of 74 with LJC media (NS, p > 0.05). Five atypical mycobacteria were isolated in the biphasic medium, 3 of which were also recovered on the LJC media. Average recovery time (ART) for Mycobacterium tuberculosis was 20.2 +/- 8.3 days and 28.4 +/- 10.6 days respectively for MB-Check and LJC media. This difference is statistically significant (p = 0.001). When considering only the samples found positive upon smear examination, the difference is more obvious: ART for M. tuberculosis is 16.6 +/- 4.4 days and 25.3 +/- 8.7 days respectively for MB-Check and LJC media (p < 0.05). Of the 14 specimens found negative upon smear examination, 12 gave a positive culture on the MB medium, vs 9 on the LJC medium (NS). Of these 12 specimens, 2 were cerebrospinal fluids which were found negative after culture on LJC media. The difference in ART between MB-Check and LJC media was not statistically significant (27.8 +/- 8.5 days vs 33.8 +/- 11.4 days) (p > 0.05).