Mycobacterium lentiflavum, a recently identified slow-growing mycobacterial species: clinical significance in immunosuppressed cancer patients and summary of reported cases of infection.

The clinical significance of Mycobacterium lentiflavum, a recently identified nontuberculous mycobacterium, remains uncertain, especially in immunosuppressed cancer patients. The records of all patients in whom M. lentiflavum was identified using a gene sequencing technique between January 2001 and December 2003 were reviewed. The mean age among 12 patients was 51+/-20 years, and 11 (92%) patients had a hematologic malignancy. Six of seven (86%) hematopoietic stem cell transplant recipients had received allogeneic donor grafts. Nine (75%) patients had predisposing risk factors for infection, seven (58%) had severe lymphocytopenia (<400 cells/microl), five (42%) were receiving systemic corticosteroid therapy, and three (25%) had acute graft-versus-host disease. Only 1 of the 12 (8%) patients had evidence of probable pulmonary M. lentiflavum infection. Six M. lentiflavum strains were initially misidentified as Mycobacterium simiae and Mycobacterium avium-intracellulare complex using traditional biochemical tests. Four M. lentiflavum isolates were tested for antimicrobial susceptibility; they were susceptible to isoniazid, ethambutol, clarithromycin, and amikacin, and resistant to rifampin. M. lentiflavum was not clinically significant, even in these severely immunosuppressed cancer patients.