Prevalence, Strains, and Drug Susceptibility of Nontuberculous Mycobacteria Isolates from Tuberculous Suspects

The prevalence of nontuberculous mycobacteria (NTM) infection has been increasing globally. Many cases of NTM infection are misdiagnosed as Mycobacterium tuberculous (MTB) because of similar clinicoradiological features.

To determine the burden and characteristics of NTM infection, this study was done to evaluate clinical isolates collected from tuberculous (TB) suspects in a population from Northwest China.

From January to December 2020, the clinical samples of 9,142 TB suspects were collected for the PCR-fluorescent probe and mycobacterial culture. The PCR-fluorescent probe-positive nucleic acid samples were further subjected to a DNA microarray for confirmation and species identification. Drug susceptibility testing (DST) was also carried out using the micropore plate method (MicroDSTTM) on isolates from NTM patients.

Of 9,412 TB suspects, 85 cases (0.9%) were clinically diagnosed with NTM infection according to the American Thoracic Society (ATS) guidelines. For the laboratory samples, a total of 169 NTM strains, identified by molecular biology methods, were classified into 10 species. Themost common species were M. chelonae/ M. abscessus (64/169, 37.7%) and M. intracellulare (40/169, 23.7%). All strains showed the highest resistance to imipenem/cilastatin (85/85, 100%) and the highest susceptibility to linezolid (4/85, 4.7%). In comparison with the rapidly growing mycobacteria (RGM) group, the slowly growing mycobacteria (SGM) group showed a lower resistance and a shorter hospital inpatient stay (t = 6.66, P < 0.001 and t = 2.40, P = 0.020, respectively).

Mycobacterium chelonae/M. abscessus and M. intracellulare were the most frequently detected NTM pathogens in Northwest China. The differences in drug sensitivity and clinical characteristics were giant for different strains. Timely identification and accurate DST play important roles in NTM management.