Same-day identification and genotypic antibiotic resistance testing of Mycobacterium tuberculosis complex and non-tuberculous mycobacteria from positive blood culture bottles – a proof of principle assessment

Background and Aims: patients suffering from systemic mycobacterial spread are at high risk of unfavorable clinical outcomes. Rapid microbiological diagnosis, however, is complicated due to the very slow cultural growth of mycobacteria. To facilitate the diagnostic workflow, we assessed a workflow allowing mass spectrometry-based identification and molecular resistance testing of mycobacteria directly from blood culture pellets.

Materials and Methods: for this study, 50 blood cultures spiked with n=10 Mycobacterium tuberculosis (MTC) isolates and n=40 isolates belonging to 12 other species of non-tuberculous mycobacteria (n=13 M. abscessus complex, n=5 M. avium, n=3 M. chimaera, n=5 M. fortuitum, n=5 M. intracellulare, n=2 M. lentiflavum and n=2 M. mucogenicum, n=1 for each one of the species M. elephantis, M. hassiacum, M. marseillense, M. nebraskense and M. parascrofulaceum) were used next to two clinical cases of a disseminated infection in HIV patients.

Results: the application of the MBT Sepsityper® kit allowed the correct species level identification by applying mass spectrometry as well as correct molecular resistance testing results as compared to the diagnostic reference approach applied with mycobacterial culture material.

Conclusions: in conclusion, the results provide a proof-of-principle of the suitability of the assessed potential workflow in order to achieve a shortened time-to-result for the diagnosis of systemic mycobacterial infections. Future studies in high endemicity settings are desirable to assess the clinical applicability and impact of such a shortened workflow.