Comparison of a novel bilayered medium with the conventional media for cultivation of Mycobacterium tuberculosis

There is resurgence of tuberculosis in recent years in spite of availability of comprehensive multidrug therapy. Conventional culture media require a long time for the appearance of growth of Mycobacterium tuberculosis, while the other methods are expensive. Hence, a rapid low cost and safe bilayered medium was developed for early growth and sensitivity testing of M. tuberculosis and the results were compared with those on Lowenstein Jensen medium, Middlebrook 7H10 and Kirchner's liquid media.

A specially designed bilayered medium, consisting of a lower layer of Lowenstein Jensen medium without malachite green and a top layer of Middlebrook 7H 10 medium with added antibiotics and antifungal agents was prepared. Sputum from clinically suspected cases of tuberculosis, pleural fluid and pus samples were inoculated on the bilayered medium along with the inoculation on other conventional media after proper decontamination and concentration of the samples. Antibiotic sensitivity pattern was determined against a few rapidly growing control and test strains by disc diffusion technique and the results could be recorded by 3 to 7 days.

Statistically significant (P< 0.001) isolation rate was obtained on this bilayered medium when compared with the other three media, being 81.7 per cent growth by 7 days. Antibiotic sensitivity test could be recorded by 3 days in case of the rapidly growing strains on this medium, and by 7 days in case of M. tuberculosis strains.

Bilayered medium produced rapid growth earliest by 48 h, higher isolation rates were achieved as compared to the other conventional media and drug sensitivity testing could also be carried out successfully. Thus, the bilayered medium can be used for obtaining early culture report.