Simple direct drug susceptibility tests on sputum samples for early detection of resistance in tubercle bacilli.
BACKGROUND
Direct sensitivity test either by sputum concentrate (DS) or swab method (DSM) set up along with the primary culture would avoid the delay of four or more weeks required for the indirect test. A comparison of these two methods against the standard indirect sensitivity method under routine laboratory conditions is necessary to prove their merit.


METHODS
Smear positive sputum samples were aliquoted and sensitivity tests were set up by both the direct methods as also an indirect test set up from the primary culture of the same sample.


RESULTS
The agreement with the indirect test results for isoniazid (INH) ranged from 97-98% for the DS method and 93-97% for the DSM method. The corresponding figures were 96-98% by the DS and 94-99% by the DSM method for rifampicin (R). The agreement was less satisfactory for ethambutol (Emb).


CONCLUSIONS
This study showed that direct sensitivity tests such as DS and DSM methods can detect most of the cultures resistant to INH and R (MDR) from the time growth appears on the primary culture, even as early as the second week of setting up the tests.
Mathew
Sarah
S
Tuberculosis Research Centre, Indian Council of Medical Research, Chetput, Chennai-600 031.
Nalini
S M
SM
Rahman
Fathima
F
Dastageer
Aszhgar
A
Sundaram
V
V
Paramasivan
C N
CN
D000995:Antitubercular Agents / Q000494:pharmacology; D004352:Drug Resistance, Microbial; D006801:Humans; D008826:Microbial Sensitivity Tests / Q000379:methods*; D009169:Mycobacterium tuberculosis / Q000187:drug effects* / Q000302:isolation & purification*; D012680:Sensitivity and Specificity; D013183:Sputum / Q000382:microbiology*
D000995:Antitubercular Agents