A Rough Colony Morphology of Mycobacterium abscessus Is Associated With Cavitary Pulmonary Disease and Poor Clinical Outcome.

Background: The Mycobacterium abscessus complex (MABC) is a difficult to treat mycobacterium with two distinct morphologies: smooth and rough. As the clinical implications are unclear, we explored the morphology of MABC in relation to disease and outcome.

Methods: We performed a retrospective multicenter cohort study including patients with confirmed MABC in Sweden, 2009-2020, with treatment outcome as the primary outcome. MABC colony morphology was determined by light microscopy on Middlebrook 7H10 agar plates.

Results: Of the 71 MABC isolates, a defined morphology could be determined for 63 isolates, of which 40 were smooth (56%) and 23 were rough (32%). Immunosuppression, pulmonary disease, and cavitary lesion on chest radiographs were significantly associated with a rough isolate morphology. Participants with smooth isolates had more favorable treatment outcomes (12/14, 86%) compared to those with rough isolates (3/10, 30%). In an age-adjusted logistic regression, rough morphology of MABC was associated to lower odds of clinical cure compared to smooth morphology (adjusted odds ratio, 0.12; P = .049).

Conclusions: Study participants with rough MABC colony morphology of isolates had a worse clinical outcome compared to those with smooth isolates. The biological mechanisms should be further characterized and colony morphology of MABC taken into account during clinical management.