Mycobacterium abscessus Smooth and Rough Morphotypes Form Antimicrobial-Tolerant Biofilm Phenotypes but Are Killed by Acetic Acid.

Gillian Clary,Sara Cole,Nathan Nesbitt,Abul Azad,Luanne Hall-Stoodley,Laurel Mason,Karen Mccoy,Larry S Schlesinger,Smitha J Sasindran

doi:10.1128/aac.01782-17

Abstract

ABSTRACTMycobacterium abscessus has emerged as an important pathogen in people with chronic inflammatory lung diseases such as cystic fibrosis, and recent reports suggest that it may be transmissible by fomites. M. abscessus exhibits two major colony morphology variants: a smooth morphotype (MaSm) and a rough morphotype (MaRg). Biofilm formation, prolonged intracellular survival, and colony variant diversity can each contribute to the persistence of M. abscessus and other bacterial pathogens in chronic pulmonary diseases. A prevailing paradigm of chronic M. abscessus infection is that MaSm is a noninvasive, biofilm-forming, persistent phenotype and MaRg an invasive phenotype that is unable to form biofilms. We show that MaRg is hyperaggregative and forms biofilm-like aggregates, which, like MaSm biofilm aggregates, are significantly more tolerant than planktonic variants to acidic pHs, hydrogen peroxide (H2O2), and treatment with amikacin or azithromycin. We further show that both variants are recalcitrant to antibiotic treatment inside human macrophage-like cells and that MaRg is more refractory than MaSm to azithromycin. Our results indicate that biofilm-like aggregation and protracted intracellular survival may each contribute to the persistence of this problematic pathogen in the face of antimicrobial agents regardless of morphotype. Biofilms of each M. abscessus variant are rapidly killed, however, by acetic acid, which may help to prevent local fomite transmission.

Highlights

Mycobacterium abscessus has emerged as an important pathogen in people with chronic inflammatory lung diseases such as cystic fibrosis, and recent reports suggest that it may be transmissible by fomites
M. abscessus Antimicrobial-Tolerant Biofilms one colony morphology variant, and we investigated each morphotype using isogenic morphology variants: a smooth morphotype (MaSm) and MaRg variants isolated from the sequenced M. abscessus ATCC 19977T reference strain [46]
The optical density at 600 nm (OD600) of isolated MaRg or MaSm grown with shaking for 48 h with or without Tween showed that MaRg settled within 15 min in the absence of Tween, whereas MaSm remained suspended during this time, indicating that MaRg was significantly more aggregative than MaSm (Fig. 1h)

Summary

Introduction

Mycobacterium abscessus has emerged as an important pathogen in people with chronic inflammatory lung diseases such as cystic fibrosis, and recent reports suggest that it may be transmissible by fomites. Biofilm formation, prolonged intracellular survival, and colony variant diversity can each contribute to the persistence of M. abscessus and other bacterial pathogens in chronic pulmonary diseases. M. abscessus can cause skin and soft tissue infections in patients with healthy immune systems, as well as a variety of infections on medical implants [1,2,3] It has recently gained attention as the most common cause of RGM infections worldwide in people with chronic inflammatory lung diseases such as cystic fibrosis (CF), non-CF bronchiectasis, and chronic obstructive pulmonary disease (COPD), resulting in both nodular and cavitary granulomas and persistent lung infection [1, 2, 4,5,6,7,8,9,10,11]. P. aeruginosa colony morphology variants isolated from CF sputum include mucoid colonies and aggregative rugose small-colony variants, both of which are linked to extended antibiotic treatment and correlate with the onset of persistent infection [25, 30]

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