Abstract
A non-tuberculous mycobacterium, Mycobacterium abscessus is an emerging opportunistic pathogen associated with difficult to treat pulmonary infections, particularly in patients suffering from cystic fibrosis. It is capable of forming biofilms in vitro that result in an increase of already high levels of antibiotic resistance in this bacterium. Evidence that M. abscessus forms biofilm-like microcolonies in patient lungs and on medical devices further implicated the need to investigate this biofilm in detail. Therefore, in this study we characterized the M. abscessus pellicular biofilm, formed on a liquid–air interface, by studying its molecular composition, and its transcriptional profile in comparison to planktonic cells. Using scanning electron micrographs and fluorescence microscopy, we showed that M. abscessus biofilms produce an extracellular matrix composed of lipids, proteins, carbohydrates and extracellular DNA. Transcriptomic analysis of biofilms revealed an upregulation of pathways involved in the glyoxylate shunt, redox metabolism and mycolic acid biosynthesis. Genes involved in elongation and desaturation of mycolic acids were highly upregulated in biofilms and, mirroring those findings, biochemical analysis of mycolates revealed molecular changes and an increase in mycolic acid chain length. Together these results give us an insight into the complex structure of M. abscessus biofilms, the understanding of which may be adapted for clinical use in treatment of biofilm infections, including strategies for dispersing the extracellular matrix, allowing antibiotics to gain access to bacteria within the biofilm.
Highlights
Non-tuberculous mycobacteria (NTM) belong to the genus Myco bacterium and are environmental bacteria capable of causing disease in immunocompromised individuals
Using scanning electron microscopy (SEM), we studied the formation of M. abscessus pellicles after a 6-day incubation
Using confocal laser scanning microscopy (CLSM), we showed that the extracellular matrix (ECM) consists of lipids, polysaccharides, proteins and extracellular DNA (eDNA) (Fig. 2), all previously reported to play integral roles in biofilm formation and maturation in various bacterial species (Rose et al, 2015)
Summary
Non-tuberculous mycobacteria (NTM) belong to the genus Myco bacterium and are environmental bacteria capable of causing disease in immunocompromised individuals. Since the discovery of the association of Mycobacterium avium infections with mortality in HIV patients, disseminated and mixed culture NTM infections were found in other immunocompromised populations suffering from chronic pulmonary disease, renal failure, cystic fibrosis (CF), leukaemia and in transplant recipients (Sousa et al, 2015). Mycobaterium abscessus is a rapidly growing NTM and an emerging opportunistic pathogen most often causing chronic pulmonary disease in patients with underlying lung conditions (Medjahed et al, 2010). M. abscessus is the most commonly isolated rapidly growing mycobacteria from lung infections, which is alarming given the average rate of treatment success is only 45.6% (Kim et al, 2016; Kwak et al, 2019). None of the currently available treatments are curative or have been shown as effective in long-term sputum conversion in patients with chronic lung disease (Kwak et al, 2019)
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