Evaluation of biphasic culture system for mycobacterial isolation from the sputum of patients with pulmonary tuberculosis.

Mycobacterial diseases continue to cause high morbidity and mortality. Isolation, identification and sensitivity testing form the backbone of laboratory investigations. M. tuberculosis isolation needs 6-8 weeks on conventional egg containing media. For rapid isolation various methods have been evaluated. We evaluated biphasic system (Middlebrook 7H11 agar slant+Middlebrook 9H broth) in comparison with Lowenstein-Jensen (LJ) medium. In smear positive cases biphasic system showed the recovery rate of 97.05% as against 79.41% on LJ on incubation for 21+/-4.44 and 28+/-3.76 days respectively. In smear negative and culture positive cases biphasic system and LJ showed isolation rates of 91.66% and 66.6% after 36+/-3.44 and 41+/- 4.09 days respectively. Biphasic system showed lower contamination rate (1.33%). Biphasic medium is superior to LJ medium in isolation of M. tuberculosis.