Mycobacterium abscessus subsp abscessus lung disease: ‘trouble ahead, trouble behind…’

Mycobacterium abscessus subsp abscessus is the most common respiratory pathogen among the rapidly growing non-tuberculous mycobacteria (NTM) and is also the most feared due to its well-deserved reputation for being refractory to antibiotic therapy. M. abscessus subsp abscessus has multiple innate antibiotic resistance mechanisms, but the most important one described so far is an inducible erythromycin methylase (erm) gene. M. abscessus subsp abscessus isolates may appear macrolide susceptible on initial in vitro testing but become macrolide resistant after exposure to macrolide. It is therefore very important to test clinically significant M. abscessus subsp abscessus isolates for erm gene activity. Remarkably, controversy still exists about the taxonomy and nomenclature of M. abscessus subspecies including subsp abscessus, subsp massiliense and subsp bolletii. Identification of these subspecies is not moot as M. abscessus subsp massiliense does not have an active erm gene resulting in both in vitro and in vivo susceptibility to macrolide. It is imperative from the clinician's perspective that mycobacterial laboratories correctly and rapidly identify M. abscessus to the subspecies level. Unfortunately, there are no reliably or predictably effective treatment regimens for M. abscessus subsp abscessus and better, more effective antimicrobial agents are badly needed. Surgical resection of involved lung tissue as an adjunct to antibiotic therapy is beneficial in selected patients but cannot be broadly applied. Overall, M. abscessus subsp abscessus remains a formidable respiratory mycobacterial pathogen, one that we are only beginning to understand microbiologically and one that as yet consistently evades our best efforts at successful therapeutic outcomes. ‘trouble ahead, trouble behind, and you know that notion just crossed my mind’. Casey Jones, Grateful Dead (1970)