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Evaluation of a new rapid kit for MALDI-TOF MS Mycobacteria identification 

A Camaggi(1) M Casagrande(1) M S Caroppo(1) S Andreoni(1)

1:AOU Maggiore della Carità, Laboratory of Microbiology and Virology – Novara, Italy

In recent decades, non-tuberculous mycobacteria (NTM) infection rates raised, due to the increased number of immunocompromised individuals. Fast and accurate identification tools are essential for an effective an appropriate treatment of NTM infections. MALDI-TOF MS has become a reliable tool for mycobacteria identification, despite their challenging cell wall structure. Here, we evaluated the new MTB Mycobacteria-IVD kit (Bruker Daltonics, Germany), based on chemical cell-inactivation and mechanical-disruption of cell aggregates, using Line Probe Assay (GenoType Mycobacterium CM/AS-Hain-Lifescience,GmbH) and/or DNA sequencing results as a reference.

Fifty various NTM species were cultured on solid and liquid media and on blood cultures bottles. A mycobacterial biomass was washed and inactivated with the ready-to-use reagents (Washing Solution, Inactivation Reagent) for 30 minutes at room temperature. After centrifugation (2 min), the pellet was mixed with formic acid and acetonitrile, vortexed and centrifuged at max-speed for 2 minutes. Supernatant (1 µL) was spotted in triplicate onto the MALDI plate. Once dried, Bruker Matrix-HCCA was added, and MALDI-TOF MS identification was performed, using Mycobacteria IVD Library v2.0. Overall, the identification was achieved in less on 45 minutes. Results interpretation was performed according to the manufacturer’s instructions: log(score) ≥ 1.80 highly-probable identification, log(score) between 1.60 and 1.79 probable identification and log(score) <1.60 not assigned identification. Identifications were correct for all NTMs examined. From liquid media culture (low biomass) identifications showed a log(score)< 1.60 but correct.

Our results suggest that Mycobacteria-IVD kit could provide a great advantage for timely and cost-saving NTMs identification with potential relevant implications for patient outcome.

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