Objective: To investigate the susceptibility of Mycobacterium intracellulare isolates to clarithromycin, azithromycin and linezolid, and therefore to explore the possibility of using these drugs to treat Mycobacterium intracellulare diseases.
Methods: The minimal inhibitory concentrations (MICs) of the 3 antibiotics against 76 Mycobacterium intracellulare isolates were determined by using microplate alamar blue assay (MABA).
Results: The MIC90 of clarithromycin against Mycobacterium intracellulare isolates was 2 mg/L. The proportion of susceptible, intermediate and resistant isolates to clarithromycin was 93.4% (71/76), 0.0% (0/76) and 6.6% (5/76), respectively. The MIC90 of azithromycin against the isolates was 32 mg/L. The proportion of susceptible, intermediate and resistant isolates to azithromycin was 94.7% (72/76), 0.0% (0/76) and 5.3% (4/76), respectively. The MIC90 of linezolid was 64 mg/L. The proportion of susceptible, intermediate and resistant isolates to linezolid was 32.9% (25/76), 22.4% (17/76) and 44.7% (34/76), respectively. Among the 5 isolates resistant to clarithromycin, 4 were resistant to azithromycin, and 2 were resistant to linezolid.
Conclusions: Most of the Mycobacterium intracellulare isolates were sensitive to clarithromycin. High cross-resistance between clarithromycin and azithromycin was present, but some clarithromycin-resistant isolates were sensitive to linezolid.