Background: Pulmonary non-tuberculous mycobacteria (NTM) represent an increasing threat as NTM infection can become chronic in susceptible patients and require heavy antibiotic treatments. Their diagnosis remains difficult due to fastidious sample preparation involving prior decontamination, slow growth and pulmonary flora that can be abundant, especially in the case of cystic fibrosis (CF) patients.
RGM medium has been designed at the Freeman Hospital (Newcastle Upon Tyne, UK). This medium shows increased specificity and sensitivity compared to reference methods.
NTM Elite agar (bioMérieux) is the industrial version derived from RGM medium dedicated to the isolation of non-tuberculous mycobacteria from respiratory specimens without prior decontamination.
Materials/methods: 50 well-characterized non-tuberculous mycobacteria strains were subcultured on both the reference medium (Coletsos) and on NTM Elite Agar. Colonies were processed in duplicate with the VITEK® MS MYCOB/NOCARDIA KIT and were analyzed by MALDI-TOF with the VITEK®MS system (KB IVD V3.2.0.). Duplicates were considered as individual tests for analysis, thus representing 100 results per tested media.
Results: The strains were identified at species or complex level for 94% on NTM Elite agar and 85% on Coletsos. The rates of no identification were 4% on NTM Elite agar and 13% on Coletsos. Duplicate spots resulted in a no identification result in only four cases for Coletsos, and only one case for NTM Elite agar. This could be explained by an easier picking of the colonies on the NTM Elite agar plates compared to the Colestos tubes, especially in the case of rough colonies. The rate of misidentification was 2% for both media and concerned only one strain.
Conclusions: Isolation of non-tuberculous mycobacteria from specimens without prior decontamination on NTM Elite agar, associated with a direct identification by MALDI-TOF VITEK®MS, enables a streamlined screening of non-tuberculous mycobacteria, thus improving patient care.