S2.3d Mixed biofilm of Aspergillus fumigatus and Stenotrophomonas maltophilia: Microscopic visualization of galactosaminogalactan and galactomannan polysaccharides in the extracellular matrix

S2.3 NOVEL DIAGNOSTIC TOOLS FOR INVASIVE MOLD INFECTION, SEPTEMBER 21, 2022, 3:00 PM - 4:30 PM: INTRODUCTION: Aspergillus fumigatus (Af) and Stenotrophomonas maltophilia (Sm) are commonly co-isolated from the airways of cystic fibrosis patients, especially in mixed biofilms. A mixed Af-Sm biofilm model, developed by our lab, demonstrated that Sm exhibits an antibiosis effect on Af by (1) inhibiting fungal growth, (2) rendering the fungal mycelia highly branched, and (3) increasing the fungal cell wall thickness.(1) The presence of three Af cell wall polysaccharides, galactomannan (GM), galactosaminogalactan (GAG), and α-1,3-glucan, have been described in the extracellular matrix (ECM) of Af biofilms.(2) GM and GAG are known to be released out from the cell wall of Af.(3) GAG contains N-acetylgalactosamines (GalNAc) which undergo partial deacetylation extracellularly, to be converted to GalN, and thus transform this polysaccharide into a polycation with strong surface binding properties.(4) AIM OF THE STUDY: Analyze the structure of fungal cell wall polysaccharides in the formation of Af biofilm alone or mixed with Sm. METHODS: The Af-Sm co-culture was prepared on an 8-chambers Lab-Tek slide as described previously(1). Anti-GAG and anti-GM monoclonal antibodies produced at the Aspergillus Unit at Pasteur Institute of Paris, were used to focus on the 3D structure of GAG and GM in the ECM of the biofilm. These polysaccharides were analyzed by fluorescence confocal microscopy at 24 h. RESULTS AND CONCLUSION: GM was found, as expected, in the hyphal Af cell wall but was very little in the ECM. GAG was also found in the cell wall but mainly formed a beautiful fibrillary network between the hyphae, showing the importance of this polysaccharide in cell-cell interaction and in the structuration of Af biofilm. GAG could be the surface receptor for Sm, which would promote strong adhesion between Sm and Af in the biofilm. SOURCES: 1. Melloul E et al. Front Microbiol. 2018; 2. Beauvais A et al. Microbiol Spectr. 2015; 3. Fontaine T et al. J Fungi. 2020; 4. Briard B et al. Mycologia 2016.