Evaluation of nutrient agar for the culture of Mycobacterium tuberculosis using the microcolony detection method

We evaluated nutrient agar using the microcolony detection method for the recovery of Mycobacterium tuberculosis on 37 acid-fast bacilli (AFB) positive sputum specimens, and compared it with conventional Löwenstein-Jensen (LJ) medium. Nutrient agar detected 35 isolates compared to 34 on LJ medium. The mean time to detection of mycobacteria on nutrient agar and LJ medium was respectively 9.6 and 21.4 days. The contamination rate on nutrient agar and LJ medium was respectively 5.4% and 2.7%. Nutrient agar detects M. tuberculosis more rapidly than LJ medium, and could be an economical, rapid culture method in resource-poor settings, provided our findings are confirmed by further studies.

Evaluation of thin-layer agar 7H11 for the isolation of Mycobacterium tuberculosis complex

We evaluated the thin-layer agar (TLA) method for the recovery of Mycobacterium tuberculosis complex and compared the results with the BACTEC Mycobacteria Growth Indicator Tube (MGIT) 960 system. A total of 53 mycobacterial isolates were isolated on both media. The recovery rates of mycobacteria on TLA and BACTEC MGIT 960 system were respectively 90.6% and 96.2%. Mean time to detection of mycobacteria on TLA was 12.5 compared to 11.2 days on BACTEC MGIT 960. TLA is a simple technique and can be used as an alternative to the Löwenstein-Jensen medium and BACTEC MGIT 960 for the isolation of mycobacteria in resource-poor settings.