Comparison of the RGM medium and the mycobacterial growth indicator tube automated system for isolation of non-tuberculous mycobacteria from sputum samples of cystic fibrosis patients in Belgium

Abstract

PurposePulmonary infections due to non-tuberculous mycobacteria (NTM) are an emerging issue in the cystic fibrosis (CF) population. Due to bacterial and fungal overgrowth, isolation of mycobacteria from the sputum samples of these patients remains challenging. RGM medium, a novel agar-based culture medium was evaluated for the isolation of NTM from sputum samples of CF patients.MethodologySputum samples were inoculated onto RGM medium and conventional Mycobacterial Growth Indicator Tube (MGIT™, Becton Dickinson, USA). Agar plates were incubated at 35 °C and growth was recorded once a week during 42 days. We compared the yield of the two media.Results217 samples were obtained from 124 CF patients. 20 samples (13 patients) had a positive culture for NTM. 79/217 (36.4%) MGIT had to be discontinued due to contamination compared to 18/217 (8.3%) for RGM. We reported equivalent NTM detection performances for RGM and MGIT (P = 0.579): these media enabled the isolation of 15 and 12 NTM strains respectively.ConclusionRGM medium increases the proportion of interpretable results and the number of NTM cultured. Taking into account the non-inferiority compared to conventional methods and ease of use of RGM medium, we estimate that this test can replace current approaches for the screening of NTM among people with CF. Additionally, RGM provides semi-quantitative results (number of colonies) and information on the morphology of colonies, which may be clinically relevant information.

Serological biomarkers for the diagnosis of Mycobacterium abscessus infections in cystic fibrosis patients

“…Recent work on a new medium makes it possible to avoid the decontamination step of the respiratory sample, with a certain increase in the sensitivity of the culture (19). However, this medium is still largely a more favorable medium for the growth of rapid-growing NTM (RGM) compared to slow-growing NTM (SGM), as shown recently, with only a 50% recovery for M. avium and M. intracellulare (20).…”

Nontuberculous Mycobacteria in Cystic Fibrosis in the Era of Cystic Fibrosis Transmembrane Regulator Modulators

“…Improvements in decontamination processes and the introduction of specific selective media have increased rates of recovery of NTM. [53][54][55][56] Culture-independent molecular methods are evolving; however, the initial assessments of 16S rRNA probes for the detection of NTM in CF sputum samples were disappointing. 57 In a recent study, focused on MABS detection from unprocessed CF sputum samples, a real-time PCR MABS detection assay, had a sensitivity of 84% and specificity of 98%; results were available days to weeks earlier than culture results.…”

Mycobacterium mageritense related peritoneal dialysis peritonitis: An antibiogram summary and successful treatment experiences

“…4 RGM medium, a new selective medium for rapidly growing mycobacteria, has been demonstrated to exhibit fair detection efficacy and ease of use. 6,7 Its wider application may facilitate earlier diagnosis of NTM-related PD peritonitis. In this case, the interval from symptom onset to culture diagnosis and antibiotic regimen revision was 25 days, and the time required for isolating M. mageritense was 10 days.…”