Drug susceptibiity testing of nontuberculous mycobacteria by broth microdilution method

Introduction: -Incidence of Nontuberculous mycobacteria (NTM) has been increasing in past few years. Treatment of NTM differs from Mycobacterium tuberculosis. For proper treatment, it's important to carry out Drug Susceptibility Testing of NTM. Method of DST for NTM is different from MTB and is not available in most laboratories. Method: -We performed DST on 122 isolates of NTM. Amikacin, Ciprofloxacin, Trimethoprim, Doxycycline, Moxifloxacin, Clarithromycin, Minocycline and Cefoxitin were used for Rapid Growing Mycobacteria (RGM) and Rifampicin, Clarithromycin, Ethambutol, Isoniazid and Moxifloxacin for Slow Growing Mycobacteria (SGM). M. avium Complex (MAC) was tested against Clarithromycin. Minimum inhibitor concentration was calculated as recommended by standard Clinical and Laboratory Standards Institute (CLSI) and Resazurin Microtitre Assay (REMA). Result: -Most of Rapid Growing Mycobacteria were sensitive to Amikacin (76.1%) and Moxifloxacin (46.47%) while Slow Growing Mycobacteria showed only 33.3% sensitivity to Rifampicin and Moxifloxacin and 42% to Clarithromycin. M. avium-intracellulare complex showed 45-50% sensitivity to Clarithromycin. Overall, 98% concordance (Kappa = 0.98; almost perfect; 95% CI = 0.966 to 0.996) was seen between standard and REMA method of DST of NTM. Conclusion: -Rapid growers showed good sensitivity to Amikacin and Moxifloxacin, while only one third SGM showed sensitivity to Rifampicin, Moxifloxacin and Clarithromycin. For proper management of NTM of eastern Rajasthan its important to know the DST profile in our area to initiate empirical therapy till the results of specific patient are available. REMA was found to give excellent concordance with standard method.

Automated summary

- The incidence of nontuberculous mycobacteria (NTM) has been increasing in recent years, with different treatment methods compared to Mycobacterium tuberculosis. Drug Susceptibility Testing (DST) of NTM is crucial for proper treatment, although the methods are different from those used for Mycobacterium tuberculosis and are not widely available. Results from DST of 122 NTM isolates showed varying sensitivities to different drugs, with rapid growing mycobacteria showing good sensitivity to Amikacin and Moxifloxacin, while slow growing mycobacteria had lower sensitivity to Rifampicin, Moxifloxacin, and Clarithromycin. The Resazurin Microtitre Assay (REMA) method of DST showed excellent concordance with the standard method, providing a useful alternative for testing NTM sensitivity.