Introduction.
Mycobacterium avium
complex (MAC) has been reported as the most common aetiology of lung disease involving nontuberculous mycobacteria.
Hypothesis. Antimicrobial susceptibility and clinical characteristics may differ between
Mycobacterium avium
and
Mycobacterium intracellulare
.
Aim. We aimed to evaluate the differences in antimicrobial susceptibility profiles between two major MAC species (
Mycobacterium avium
and
Mycobacterium intracellulare
) from patients with pulmonary infections and to provide epidemiologic data with minimum inhibitory concentration (MIC) distributions.
Methodology. Between January 2019 and May 2020, 45
M. avium
and 242
M
.
intracellulare
isolates were obtained from Shanghai Pulmonary Hospital. The demographic and clinical characteristics of patients were obtained from their medical records. The MICs of 13 antimicrobials were determined for the MAC isolates using commercial Sensititre SLOWMYCO MIC plates and the broth microdilution method, as recommended by the Clinical and Laboratory Standards Institute (CLSI; Standards M24-A2). MIC50 and MIC90 values were derived from the MIC distributions.
Results.
M. intracellulare
had higher resistance rates than
M. avium
for most tested antimicrobials except clarithromycin, ethambutol, and ciprofloxacin. Clarithromycin was the most effective antimicrobial against both the
M. avium
(88.89 %) and
M. intracellulare
(91.32 %) isolates, with no significant difference between the species (P=0.601). The MIC90 of clarithromycin was higher for
M. avium
(32 µg ml−1) than
M. intracellulare
(8 µg ml−1). The MIC50 of rifabutin was more than four times higher for
M. intracellulare
(1 µg ml−1) than
M. avium
(≤0.25 µg ml−1). The percentages of patients aged >60 years and patients with sputum, cough, and cavitary lesions were significantly higher than among patients with
M. intracellulare
infection than
M. avium
infections.
Conclusions. The pulmonary disease caused by distinct MAC species had different antimicrobial susceptibility, symptoms, and radiographic findings.