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Clinical challenges and culture-based diagnostics

Performance of the NTM Elite agar* for the detection of non-tuberculous mycobacteria in sputum samples of patients with cystic fibrosis

April 20 • P2407

E. André1, L. Raymaekers1, S. Deiwick2, J. Gafsi3, P. Van Bleyenbergh4, L. Dupont4, B. C. Kahl2, N. Lorent4

1) Laboratory of Clinical Bacteriology and Mycology, Department of Microbiology, Immunology and Transplantation, KU Leuven, Leuven, Belgium
2) University Hospital Muenster, Institute of Medical Microbiology, Muenster, Germany
3) bioMérieux, Global Clinical Affairs, Marcy l’Etoile, France
4) Pulmonology Department, KU Leuven, Leuven, Belgium

*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.

microbiology

Culture media

Paper poster