A simplified method for preparing drug susceptibility

plates has also been developed. This method uses filter

paper disks containing the primary antitubercular drugs,

and the test for susceptibility is run in a similar fashion

as the Kirby Bauer method for routine drug susceptibility

tests.

As discussed, the direct mycobacterial susceptibility

test is inoculated from digested and concentrated sputum

found to be positive for acid-fast bacilli. The indirect

susceptibility test is inoculated from colonies isolated

from a primary culture. The direct test will usually give

good results only if large numbers of mycobacteria are

present in the specimen. The advantage of the direct

susceptibility test is an earlier report (3 to 4 weeks) in

contrast to the indirect test, which may take up to 6 to 8

weeks. The disadvantage of the direct susceptibility test is

that it usually requires a large number of mycobacteria for

successful growth and is often overgrown by large numbers

of contaminating bacteria.

Other novel methods of susceptibility testing have been

developed based on the mycobacteriophage technique,

using the luminescent luciferase activity. Other researchers

have localized specific Mycobacterium tuberculosis

mutations responsible for drug resistance. These sites have

been used as amplification targets and promise to provide

a rapid method for testing the susceptibility of patient

isolates to these drugs.

PRIMARY/SECONDARY DRUG CONTAINING

LOWENSTEIN-JENSEN MEDIA PANEL MTB

SENSITIVITY TESTS

(Courtesy: Tulip Group of Companies)

Sensicult®