Unique Features of Mycobacterium abscessus Biofilms Formed in Synthetic Cystic Fibrosis Medium.

Juan M Belardinelli,Elena Lian,Zuzana Palčeková,Shiva K Angala,Victoria Jones,Vinicius C N De Moura,Jerry A Nick,Kevin H Martin,Charlotte Avanzi,Rebecca M Davidson,Bradley R Borlee,Mary Jackson,Bhanupriya Angala,Crystal J Wiersma,Mercedes Gonzalez-Juarrero,Callan Kerns,Wei Li

doi:10.3389/fmicb.2021.743126

Abstract

Characterizing Mycobacterium abscessus complex (MABSC) biofilms under host-relevant conditions is essential to the design of informed therapeutic strategies targeted to this persistent, drug-tolerant, population of extracellular bacilli. Using synthetic cystic fibrosis medium (SCFM) which we previously reported to closely mimic the conditions encountered by MABSC in actual cystic fibrosis (CF) sputum and a new model of biofilm formation, we show that MABSC biofilms formed under these conditions are substantially different from previously reported biofilms grown in standard laboratory media in terms of their composition, gene expression profile and stress response. Extracellular DNA (eDNA), mannose-and glucose-containing glycans and phospholipids, rather than proteins and mycolic acids, were revealed as key extracellular matrix (ECM) constituents holding clusters of bacilli together. None of the environmental cues previously reported to impact biofilm development had any significant effect on SCFM-grown biofilms, most likely reflecting the fact that SCFM is a nutrient-rich environment in which MABSC finds a variety of ways of coping with stresses. Finally, molecular determinants were identified that may represent attractive new targets for the development of adjunct therapeutics targeting MABSC biofilms in persons with CF.

Highlights

To establish an in vitro model of biofilm formation that mimics as closely as possible the environment encountered by Mycobacterium abscessus complex (MABSC) in the airway and lung of persons with cystic fibrosis (CF), we used a modified synthetic CF medium based on the composition of expectorated sputum (Turner et al, 2015) to grow MABSC biofilms in 96-well poly-D-lysine-coated plates
MABSC grows as submerged biofilms firmly attached to the bottom of the wells in this model allowing for reproducible quantification of biofilm formation by CFU counting (Figure 1A) and crystal violet staining (Figure 1B) over time
The studies reported highlight the importance of studying MABSC biofilms under conditions that mimic those encountered by the bacterium during host infection since different in vitro biofilm models lead to significantly different conclusions with regards to the nature of the critical constituents of the extracellular matrix (ECM) and the way MABSC biofilms respond to environmental cues

Summary

Introduction

Over the last 10 years, rapidly growing nontuberculous mycobacteria (NTM) of the Mycobacterium abscessus complex (MABSC) have emerged as important human pathogens causing an increasing number of pulmonary infections among cystic fibrosis (CF) and non-CF bronchiectasis patients globally (Floto and Haworth, 2015; Park and Olivier, 2015; Martiniano et al, 2019).Like other mycobacterial pathogens, MABSC species are intracellular pathogens that primarily infect macrophages but can target neutrophils, epithelial cells, and endothelial cellsMycobacterium abscessus Biofilms (Davidson et al, 2011; Garcia-Perez et al, 2011; Malcolm et al, 2013; Viljoen et al, 2017; Matsuyama et al, 2018). Over the last 10 years, rapidly growing nontuberculous mycobacteria (NTM) of the Mycobacterium abscessus complex (MABSC) have emerged as important human pathogens causing an increasing number of pulmonary infections among cystic fibrosis (CF) and non-CF bronchiectasis patients globally (Floto and Haworth, 2015; Park and Olivier, 2015; Martiniano et al, 2019). MABSC biofilms may further promote the colonization of the respiratory epithelium as recently illustrated by studies on Mycobacterium avium (Yamazaki et al, 2006; Babrak et al, 2015a,b) or attenuate phagocytic cell (Rose and Bermudez, 2014) and neutrophil functions (Malcolm et al, 2013) to facilitate immune evasion leading to persistent infection (Richards and Ojha, 2014)

Methods

Results

Conclusion