massiliense

Massiliense, formally Mycobacterium massiliense, is a species of rapidly growing, non-tuberculous mycobacteria within the Mycobacterium abscessus complex. It is closely related to Mycobacterium abscessus sensu stricto and Mycobacterium bolletii and, together with them, forms a group of environmental mycobacteria that can cause opportunistic infections in humans. The name massiliense honors Massilia, the Latin name for Marseille, where the organism was first described.

Taxonomy and discovery

M. massiliense is part of the family Mycobacteriaceae. It was recognized as a distinct species in the early 2010s, having been previously classified as a subspecies of M. abscessus. The taxonomic distinction relies on genetic and phenotypic analyses that differentiate it from other members of the complex.

Ecology and clinical relevance

Massiliense is found in environmental sources such as water and soil and can cause a range of clinical infections. In humans, it is associated with pulmonary disease that can resemble other forms of nontuberculous mycobacterial lung disease, as well as skin and soft tissue infections, postsurgical wound infections, and disseminated disease in immunocompromised individuals.

Diagnosis and treatment

Laboratory identification relies on molecular methods to distinguish M. massiliense from other M. abscessus complex members, including sequencing targets such as rpoB and hsp65, and, increasingly, MALDI-TOF mass spectrometry. A key clinical feature is the status of the erm(41) gene: in M. massiliense, this gene is typically nonfunctional, leading to a lack of inducible macrolide resistance and generally better responses to macrolide-containing regimens than seen with M. abscessus sensu stricto.

Treatment is usually prolonged and involves a macrolide plus additional antibiotics (e.g., amikacin, cefoxitin, or imipenem), with consideration of surgical intervention in some cases.