Drug Susceptibility of 33 Reference Strains of Slowly Growing Mycobacteria to 19 Antimicrobial Agents.

Objectives . Slowly growing mycobacteria (SGM) are prevalent worldwide and cause an extensive spectrum of diseases. Methods . In this study, the antimicrobial susceptibility of 33 reference strains of SGM to 19 antimicrobial agents was tested using a modified microdilution method. Results . Cefmetazole (32/33) and azithromycin (32/33) exhibited the highest antimicrobial activity, and dapsone (9/33) exhibited the lowest activity against the tested strains. Cefoxitin (30/33), cefoperazone (28/33), and cefepime (28/33) were effective against a high proportion of strains, and macrolides were also highly effective as well as offering the benefit of convenient oral administration to patients. Linezolid (27/33), meropenem (26/33), sulfamethoxazole (26/33), and tigecycline (25/33) showed the highest activity; clofazimine (20/33) and doxycycline (18/33) showed intermediate activity; and rifapentine (13/33), rifabutin (13/33), and minocycline (11/33) showed low antimicrobial activity, closely followed by thioacetazone (10/33) and pasiniazid (10/33), against the tested organisms. According to their susceptibility profiles, the slowly growing species Mycobacterium avium and Mycobacterium simiae were the least susceptible to the tested drugs, whereas Mycobacterium intracellulare , Mycobacterium asiaticum , Mycobacterium scrofulaceum , Mycobacterium szulgai , Mycobacterium branderi , and Mycobacterium holsaticum were the most susceptible. Conclusions . In summary, cephalosporins and macrolides, particularly cefmetazole, azithromycin, clarithromycin, and roxithromycin, showed good antimicrobial activity against the reference strains of SGM.