Drug susceptibility profiles of Mycobacterium tuberculosis isolates at Mangalore

Tuberculosis (TB) remains one of the major causes of death from a single infectious agent worldwide. Its resurgence in 1990s is primarily due to co-infection with HIV and the emergence of multi-drug-resistant (MDR) strains. Our objectives in this study were demonstration and grading of acid-fast bacilli in smears from sputum specimens of clinically newly diagnosed pulmonary TB patients, isolation of the organism, speciation and drug susceptibility testing of Mycobacterium tuberculosis isolates to isoniazid (H), rifampicin (R), streptomycin (S), and ethambutol (E).

Sputum specimens were collected from 150 patients. Smear examination was done after Ziehl-Neelsen staining. The specimens were cultured onto Lowenstein Jensen media after Petroff's method of concentration. The growth was identified as M. tuberculosis with standard tests. Sensitivity of 50 isolates of tubercle bacilli to anti-TB drugs H, R, S, E were determined by Resistance-Ratio method.

Out of 150 sputum specimens examined, 62(41.3%) were smear positive. Out of these 62,56 grew on culture. 50 isolates of M. tuberculosis were picked up for drug susceptibility testing. Total of 31 (62%) were resistant to S, 14(28%) to H, 9(18%) to R, 6(12%) were resistant to E and 2 strains (4%) were resistant to H and R.

From the small cohort, incidence of primary MDR-TB was found to be 4% in this region, which is within the expected range.