Mycobacterium chelonae infection of a cardiovascular bioprosthesis linked to a recent outbreak

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OBJECTIVES: Mycobacterium chelonae is a rapid-growing non-tuberculous mycobacterium that has occasionally been described in connection with foreign material infections, e.g. after orthopaedic joint replacement or cosmetic surgery. In a recent outbreak, several cases of M. chelonae endocarditis associated with biological heart valve prostheses were reported. CASE HISTORY: A 64-year-old female patient with a history of myalgia and recurrent joint swelling presented to our hospital. Initially suspected for rheumatoid arthritis, the patient underwent a series of orthopedic and rheumatologic treatments, including prednisolone and methotrexate. Subsequent history revealed a Ross operation in 2014 and a PET-CT was suspicious of a biological valved conduit infection leading to surgical replacement. Utilizing fluorescence in situ hybridization (FISH) diagnostic techniques, DAPI, Kinyoun and Ziehl-Neelsen staining, mycobacterial infection was confirmed in both the prosthesis and adjacent muscle tissue. Molecular methods identified a mycobacterium most closely related to the M. chelonae/abscessus complex indicating an association to a previously described outbreak of M. chelonae contaminated heart valves. Antimycobacterial therapy was initiated and the patient remains stable at the time of writing. To date, all mycobacterial cultures remained negative. CONCLUSIONS: Non-tuberculous mycobacteria (NTM) are rare and possibly underdiagnosed pathogens in infections of bioprosthetic flap bearing conduits. Mycobacterial foreign-body infections can manifest many years after implantation. As NTM can be difficult to detect, molecular identification methods are of particular importance. Here, modern imaging, molecular and microscopic techniques might be of special use in diagnosing prolonged prosthetic graft infections.

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