First reported recovery and genomic characterization of a previously uncharacterized Mycobacterium species from human blood cultures in an immunocompromised patient: a case report

Mycobacteremia is an uncommon opportunistic infection in immunocompromised hosts. We report the recovery of a previously uncharacterized Mycobacterium species from two independent blood culture sets obtained from an immunocompromised patient with persistent fever. She presented with persistent fever, and two independent blood culture sets yielded a Mycobacterium species. No focal source of infection was identified. Initial identification by MALDI-TOF mass spectrometry suggested Mycobacterium diernhoferi ; however, species-level identification could not be confirmed by molecular methods. Whole-genome sequencing demonstrated that the isolate could not be assigned to any currently recognized Mycobacterium species. Average nucleotide identity analysis showed 90.5% similarity to M. diernhoferi and 84.4% to Mycobacterium frederiksbergense , suggesting a previously uncharacterized species. Combination antimicrobial therapy was followed by resolution of fever and no recurrent positive blood cultures during treatment. Although the patient ultimately died because of progression of the underlying hematological malignancy, the patient showed sustained clinical improvement without recurrent positive blood cultures during therapy. To our knowledge, this is the first reported recovery of this genomically distinct Mycobacterium species from human blood cultures. This case highlights the value of whole-genome sequencing in recognizing previously uncharacterized Mycobacterium species recovered from human blood cultures. The pathogenic role of this organism requires further investigation.