Time to identify and define non-tuberculous mycobacteria in a tuberculosis-endemic region

OBJECTIVE: To identify and characterise disease caused by non-tuberculous mycobacteria (NTM) in a tuberculosis-endemic region.

MATERIAL AND METHODS: A total of 133 NTM isolates cultivated using Mycobacteria Growth Indicator Tube 960 (MGIT 960) plus Löwenstein-Jensen (LJ) and identified using the NAP and PNBA tests were screened to species level using molecular methods. The 360-base pair (bp) region of the rpoB gene was amplified and analysed using an in-house RLBH assay, PCR-RE and sequencing. The clinical significance of all isolated NTM was determined as per published guidelines.

RESULTS AND DISCUSSION: Of the 133 isolates, 127 were confirmed as NTM and six as Mycobacterium tuberculosis complex by molecular methods; 81% of the NTM were recovered from pulmonary and 19% from extra-pulmonary specimens. Among the rapidly growing NTM, M. fortuitum (41%) and M. abscessus (59%) were predominant. Among the slow growing NTM, 40% were identified as M. intracellulare, followed by M. simiae (35%), M. kansasii (6%), M. gordonae (4%) M. szulgai (2%) and M. avium (1%). Mixed infections were noted in 10 (12%) cases. In all, 58 (46%) NTM met clinical, radiological and microbiological criteria and were considered definite NTM infections, 33 (26%) were highly probable disease and 36 (28%) were possible disease or colonisation.

CONCLUSION: Overall, 72% of isolated NTM were found to be clinically significant. Accurate species identification and adherence to published guidelines help to outline pathogenicity.