Symbiont in circulation: Mycetohabitans endofungorum bacteremia heralding invasive mucormycosis

BACKGROUND: Bacterial endosymbionts contribute to Mucorales virulence but are rarely recognized in human infection. We describe the first clinically characterized case of Mycetohabitans endofungorum isolated from blood preceding disseminated mucormycosis. CASE: A 47-year-old immunocompetent man developed fulminant hepatitis. During pre-transplant evaluation, imaging revealed pulmonary nodules and a thoracic aortic mycotic aneurysm. Blood cultures grew an unidentifiable gram-negative coccobacillus with Vibrio-like morphology. Bronchoalveolar lavage and induced sputum cultures grew Rhizopus species. Despite maximal medical therapy, he was not a surgical candidate because of extensive vascular involvement. Subsequent 16S sequencing identified the bloodstream isolate as M. endofungorum, an obligate intracellular endosymbiont of Mucorales fungi. DISCUSSION: Isolation of M. endofungorum in blood may signal invasive mucormycosis. Even in patients without published risk factors, transient physiologic stress and barrier disruption may permit fungal invasion. Early recognition of bacterial endosymbionts could provide a valuable diagnostic clue in invasive fungal disease.