*Investigational Use Only. Performances establishment ongoing
Introduction: Non-tuberculous mycobacteria (NTM) are emerging pathogens among people with cystic fibrosis (CF). Particularly Mycobacteroides abscessus has been associated with accelerated clinical decline. Nevertheless, NTM colonization and infection is under-reported due to other bacteria resisting the NALC-NaOH decontamination used prior to conventional mycobacterial cultures, possibly resulting in masking of NTM. The NTM Elite agar (bioMérieux, France) is a novel selective agar aiming to facilitate the culture of NTM without prior decontamination of sputum samples.
Material and methods: We performed a prospective, multi-center study to compare the performance of NTM Elite agar with conventional culture methods for mycobacteria including Löwenstein-Jensen (LJ, bioMérieux, France) and Bactec MGIT (Becton Dickinson, USA). NALC-NaOH decontamination method was used prior to culture on LJ and in MGIT, while sputum samples were inoculated on the NTM Elite agar directly or after non-selective fluidization. Compared to MGIT and LJ which are incubated at 35-37°C, NTM Elite plates are incubated at 30°C, under which conditions the growth of M. tuberculosis is inhibited. This new medium can therefore be incubated and processed in conventional level 2 biosafety conditions.
Results: These preliminary results are based on 153 sputum samples from 117 patients. NTM Elite agar allowed to recover 8 positive NTM cultures (5 M. chelonae, 1 M. abscessus, 1 Mycobacterium avium, 1 other NTM), compared to 3 positive cultures for MGIT (1 M. chelonae, 2 M. avium), and no positive cultures with the LJ medium. Overall, 12% of cultures on NTM Elite agar presented an overgrowth with other micro-organisms, while this proportion was 40% on MGIT and 56% on LJ.
Conclusion: NTM Elite agar, a mycobacterial culture agar which does not require prior NALC-NaOH decontamination, outperforms conventional mycobacterial culture methods for the recovery of NTM from the sputum of CF patients. Therefore, this new medium may be considered as a suitable alternative to current time- consuming methods which still need to be considered when tuberculosis is suspected, and which are typically performed in strict level 3 biosafety conditions, what is not required for working with NTM.