Bilayered Medium for Rapid Isolation of Mycobacterium tuberculosis.

Background: A bilayered medium (BLM) seemed to indicate a rapid recovery time from Mycobacterium tuberculosis (M. tuberculosis) for the patients in question, namely, 48 hours.

Method: Sputum specimens collected from 112 patients with clinically suspected pulmonary tuberculosis were subjected to Ziehl-Neelsen staining and inoculation on Löwenstein-Jensen medium (LJM) and BLM.

Results: BLM grew all the 36 (100%) smear positive samples, while LJM grew only 20 (55.5%). On the first 2 days of incubation, BLM grew M. tuberculosis colonies in 14 specimens and in 36 specimens after 3 to 6 days. From the seventh day until the end of the incubation period, BLM grew M. tuberculosis in only 9 specimens. The mean (SD) time for detection on BLM was 6 (5) days, whereas on LJM, it was 22 (12) days.

Conclusions: BLM is more sensitive than LJM in positive and negative smears. It was also much faster than other methods in detecting the presence of M. tuberculosis.