Rapid identification of non-tuberculosis mycobacteria in simulated positive blood cultures with MALDI-TOF MS and...

Non-tuberculosis mycobacteria (NTM) cause bloodstream and disseminated infections, for which early treatment initiation following accurate pathogen identification is critical. Rapid identification using MALDI-TOF MS and the PCR-reverse sequence-specific oligonucleotide (PCR-rSSO)-based mycobacteria detection panel are potentially useful. However, their direct application to NTM-positive blood cultures has not been evaluated. We aimed to assess the feasibility of applying these assays directly to blood culture broth without prior subculturing.

Simulated blood culture broth samples with 10 NTM species-comprising type strains and clinical isolates-were prepared. Identification accuracy was assessed by comparison with the reference identifications based on type strains or whole-genome sequencing.

A total of 34 samples were prepared; Mycobacterium haemophilum was excluded because of identification-related quality issues, leaving 31 samples for analysis. MALDI-TOF MS showed 67.7% concordance with reference identifications (kappa coefficient, 0.64 [95% confidence interval (CI), 0.46-0.82]), with a higher concordance in rapidly growing mycobacteria (RGM) than in slowly growing mycobacteria (SGM). Concordance rates were 100% (kappa coefficient, 1.0) for RGM and 16.7% (kappa coefficient, 0.13 [95% CI, -0.03-0.29]) for SGM. Meanwhile, the PCR-rSSO panel achieved 87.1% overall agreement with the reference identifications (kappa coefficient, 0.86 [95% CI, 0.73-0.99] and enabled rapid detection of RGM and SGM, except for Mycobacterium mageritense, which was not covered by this panel.

MALDI-TOF MS provided accurate identification of RGM, whereas the PCR-rSSO panel demonstrated high identification performance for RGM and SGM. These methods are complementary; their combined utility warrants further evaluation in clinical settings.