Are we overlooking infections owing to non-tuberculous mycobacteria during routine conventional laboratory investigations?

Abstract

A large number of potentially pathogenic non-tuberculous mycobacteria (NTM) encountered in the clinical laboratory makes it necessary to identify their species to ensure appropriate treatment. However, labor-intensive conventional methods of speciation are not used in every laboratory, and hence NTM infections are often ignored. Polymerase chain reaction (PCR) restriction analysis (PRA) was applied in this study for early identification and speciation of mycobacterial species on 306 cultures of acid-fast bacilli isolated from patients suspected of suffering from tuberculosis. Mycobacterium tuberculosis was identified in 85.6% of the isolates. The NTM isolated most commonly was Mycobacterium kansasii/gastri group (3.5%), followed by Mycobacterium fortuitum (3.2%). Four of the M. fortuitum were grown from cultures obtained on the same day, but from samples from different patients and were probably laboratory contaminants. Mycobacterium intracellulare and Mycobacterium avium were identified in 2.94% and 2.28% of the isolates, respectively. Three isolates of M. avium and two isolates of M. intracellulare were obtained in repeated cultures from sputum samples of the same patients and were thus pathogenic. A single isolate of Mycobacterium abscessus was obtained from a breast abscess. A rare pathogen Mycobacterium phocaicum was isolated from one patient with epididymitis. However, whether it was the causative agent of epididymitis in this patient remains doubtful. The results of this study highlight the importance of speciation of mycobacteria for appropriate diagnosis and the importance of including molecular assays to augment conventional methods of diagnosis of mycobacterial diseases for rapid identification of NTM so that these potential pathogens are not overlooked in routine diagnostic procedures.