Drug Resistance Tests for Mycobacterium Tuberculosis and Compatibility between Tests; From Past to Today

Abstract

Objective: The gold standard for pulmonary tuberculosis diagnosis is the demonstration of Mycobacterium tuberculosis bacilli. Drug susceptibility test results of the bacilli obtained are crucial in tuberculosis treatment management. The various tests used to determine drug susceptibility must yield the same result. In the present study, we aimed to evaluate the compatibility of drug susceptibility test results obtained by Löwenstein-Jensen (L-J) and BACTEC 460TB methods from the past to the present.

Material and Methods: Sputum results from 79 patients suspected of multidrug-resistant pulmonary tuberculosis (MDR-TB) clinically, radiologically, and bacteriologically were evaluated for isoniazid, rifampicin, ethambutol, and streptomycin between June 1997 and June 1998. Culture and drug sensitivity tests on the L-J medium were conducted at the Heybeliada Chest Diseases and Thoracic Surgery Center bacteriology laboratory, while culture and drug sensitivity tests with the BACTEC 460 TB system were performed at another center. The results were assessed for compatibility using the Kappa (κ) test, a tool for comparing two independent parameters.

Results: All drug sensitivity tests for isoniazid, rifampicin, ethambutol, and streptomycin were collectively evaluated. It was determined that 263 (83.3%) of 316 drug sensitivity tests yielded concordant results, while 53 (16.7%) produced discordant results. The drug sensitivity tests using L-J and BACTEC 460TB methods indicated compatibility only for streptomycin (κ = 0.715). In contrast, they yielded different results for isoniazid (κ = 0.585), ethambutol (κ = 0.552), and rifampicin (κ = 0.507). Streptomycin exhibited compatibility, while isoniazid, ethambutol, and rifampicin showed incompatibility between the L-J and BACTEC 460TB methods.

Conclusion: Drug sensitivity tests are pivotal in tuberculosis treatment management. While literature suggests compatibility between L-J and BACTEC 460TB methods, our study revealed incompatibility. Evaluation of drug sensitivities may lead to confusing results. Current practices involving studies in the same laboratory and genetic testing contribute to faster and more accurate outcomes in managing drug-resistant tuberculosis. Genetic tests and reference laboratories remain crucial for antituberculosis drug sensitivity, emphasizing their continued importance.