Patterns of isolation and drug sensitivity in non-tuberculous mycobacteria

Background: Pulmonary infection with non-tuberculous mycobacteria (NTM) is a challenging and increasingly common disease. Whilst in vitro drug sensitivity generally correlates poorly with clinical outcome, in some species drug resistance is associated with treatment failure. Aim: To describe the pattern of NTM isolation and drug resistance in our centre over a 13-year period Methods: Mycobacterial culture results were retrieved from a database covering the period January 2000 – June 2014 Results: Data was obtained for 109,311 samples (31,758 subjects) of which 5,956 samples (1,205 subjects) isolated NTM. The number of subjects with a new NTM isolate increased from 62 in 2000 to 159 in 2013. Over half (54%) of subjects with respiratory isolates met ATS 2007 microbiology criteria, varying from 66% with M. abscessus to 20% with M. fortuitum . The criteria were met for >1 species in 5.5% of subjects. Drug sensitivity testing was performed on 2,794 isolates (913 subjects). Clarithromycin resistance was seen in 7% of M. abscessus and 19% of MAC isolates, though the proportion of resistant MAC fell over time to only 2.8% in 2013. The most resistant species were M. simiae and M. abscessus. Most M. simiae isolates were macrolide resistant and consistently sensitive only to clofazimine, amikacin and cycloserine. Most M. abscessus was sensitive to macrolides, aminoglycosides and tigecycline. Conclusion: NTM isolation is increasingly common. For most species resistance to key agents clarithromycin and amikacin was rare. M. simiae and M. abscessus were frequently sensitive to clofazimine and tigecycline respectively. These agents may be useful in the treatment of resistant species.