Evaluation of Culture Media for Isolation of Mycobacterium Species from Human Clinical Specimens

Background: Laboratory diagnosis of tuberculosis has undergone a rapid change during last few years and a number of techniques for culture as well as molecular diagnosis have been used with their respective advantages and disadvantages. Sporadic studies have also reported the isolation of M. tuberculosis on standard blood agar (BA), which at one time was not considered as a suitable medium for mycobacterial culture. The present study was conducted to evaluate the routine use of 5% sheep BA in a mycobacteriology laboratory by comparing isolation rates and time for isolation of mycobacteria from pulmonary and extrapulmonary samples with those on Lowenstein-Jensen (LJ) medium. Material and Methods: BA with antibiotics was prepared and dispensed as slants in McCartney bottles. LJ was prepared and dispensed following the Revised National Tuberculosis Control Programme (RNTCP) guidelines. A total of 500 suspected tuberculosis samples were inoculated on both media in duplicate, incubated at 37(0)C, and observed daily until the appearance of growth. Results: Out of 500 inoculated samples, 99 showed growth on BA and 112 showed growth on LJ medium. Mean growth time on BA was less as compared to LJ medium. The contamination rate was found to be more on BA (7.2%) than on LJ (4.8%). Conclusions: Mycobacterial growth time was less on BA as compared to LJ.