Culture of clinical samples increase the detection of Mycobacterium tuberculosis in patients and are more sensitive than direct microscopic examination. Only 10 to 100 viable organisms are needed to have a positive culture, while a minimum of 5000 to 10.000 acid-fast bacilli per milliliter are required for detection by direct smear.
Thin layer agar (TLA) use a solid medium and is based on the microscopic detection of early mycobacterial growth. This method is able to detect growth within 9–14 days and also allows the initial identification of M. tuberculosis on the basis of its colony morphology. The sample is inoculated on a plate containing Middlebrook 7H11 and Middlebrook 7H11 enriched with PNB (para-nitrobenzoic acid). The detection of growth and its comparison in the two media will help the identification of M. tuberculosis complex since it is expected to grow on 7H11 but not on 7H11+PNB where its growth will be inhibited.
Other recent developments for the rapid detection of mycobacteria include manual methods like the MB-Redox (Heipha Diagnostika Biotest, Heidelberg, Germany) based on the reduction of a tetrazolium salt indicator in liquid medium, and automated equipment-based methods like the MB/BacT system (Organon Teknika, Boxtel, Holland) based on the colorimetric detection of carbon dioxide produced by mycobacterial growth in a closed system, and the ESP culture system II (Trek Diagnostics, Inc., Cleveland, OH, USA) based on the detection of pressure changes in the culture medium of a sealed vial during mycobacterial growth. These systems have not gained widespread use outside laboratories in industrialized countries.
Maysaa El Sayed Zaki-Mycobacterium Tuberculosis, Current status in Rapid Laboratory Diagnosis -ASIN: B0056HRJI8
