Study of Resistance to First-Line Drugs in Multidrug Resistance Tuberculosis Suspects From Sputum Samples by Gold Standard – Standard Economic Variant 1% Proportion Method in North Coastal Andhra Pradesh

Abstract

Objectives: The objectives of the study were to culture Mycobacterium tuberculosis from sputum samples of multidrug resistance (MDR) suspects on Lowenstein-Jensen (LJ) media, to test for susceptibility and resistance to first-line antitubercular drugs rifampicin (RMP), isoniazid (INH), streptomycin (SM), and ethambutol (EMB) by conventional DST on LJ media by standard economic variant proportion (1%) method and to calculate the rate of MDR and pattern of drug resistance in MDR tuberculosis (MDR-TB) suspects. Methods: A prospective, laboratory-based study was done on a total of 80 samples from cases of suspected pulmonary and extra-pulmonary TB. Identification of culture isolates as M. tuberculosis was done by susceptibility to p-nitrobenzoic acid (PNB), niacin test, and catalase activity at 68°C/pH 7. Drug sensitivity testing (DST) of M. tuberculosis cultures on LJ medium for drugs was performed by a standard economic variant of the 1% proportion method. Results: Among MDR suspects, the maximum is in the age group of 45–60 years (35%) with a mean age of 42.75±15.93 years. The sex ratio of male to female is 2:1. Out of 80 samples, 36 samples (45%) were graded 1+, 31 samples (38.7%) 2+, and 13 samples (16.3%) 3+. All 80 sputum samples showed growth on LJ media within 8 weeks. When colonies obtained on LJ medium were subjected to biochemical tests for identification, all were positive for M. tuberculosis. Out of 80 M. tuberculosis isolates tested for sensitivity against first-line drugs (except pyrazinamide), 45 (56.3%) were found to be sensitive to all four drugs (INH, RMP, EMB, and SM), and 35 (43.7%) were resistant to at least one drug. Nine isolates (11.3%) showed resistance to a single drug (monoresistance). The various MDR patterns were INH+RMP seen in 6 strains (7.5%) and INH+RMP+SM seen in 4 strains (5%). Conclusion: Drug resistance trends must be closely monitored to evaluate the efficiency of existing therapies and their effect on pulmonary tuberculosis epidemic. To design the new drug regulations, more extensive data on drug sensitivity with standardized testing protocols which is quality assured are required.