Selective rapid growing mycobacterium media improves non-tuberculous mycobacteria detection and guides clinical management in Cystic Fibrosis

Abstract Trends in the isolation of non-tuberculous mycobacteria (NTM) in people with cystic fibrosis (pwCF) have varied following the introduction of CF transmembrane conductance regulator modulator (CFTRm) therapy. Standard culture methods require decontamination processes that may reduce mycobacterial viability, potentially masking true NTM prevalence. We hypothesised these methodological limitations could explain reduced yields of NTM rather than genuine reductions in overall burden. 150 respiratory samples from 73 adults and 24 paediatric pwCF were processed in parallel using MGIT, Löwenstein-Jensen (LJP), and Rapid Growing Mycobacteria (RGM) selective media. MGIT and LJP underwent standard decontamination, while RGM media did not. Clinical impact was assessed through imaging, treatment decisions, and infection-control measures. RGM media markedly increased NTM recovery, detecting NTM in 20% of samples compared with 7.3% (MGIT) and 2.7% (LJP). RGM media isolated ≥ 9 species including M. abscessus ( n = 14) and M. chelonae ( n = 11), with 38% of detections occurring exclusively on RGM media. Contamination rates were lowest with RGM media (2%). Among adults, 26% isolated NTM, with 63% representing index isolations with most adults receiving CFTRm therapy. HRCT imaging identified features consistent with NTM-pulmonary disease in most individuals with two commencing targeted therapy. RGM media provided a 125% relative increase in rapid-growing NTM recovery compared with standard methods, exceeding predefined validation thresholds. Although RGM media have been shown to increase NTM yield in pwCF, limited data exists from the CFTRm era. Incorporating RGM media into routine CF microbiology in this setting substantially enhanced NTM detection. This increased detection prompted additional clinical evaluation and surveillance in our cohort. Wider evaluation of these findings is warranted to evaluate the efficacy of RGM media in pwCF.