Purpose: Aspergillus fumigatus (Af) and Stenotrophomonas maltophilia (Sm) can coexist to form a biofilm, especially in the respiratory tract of immunocompromised or cystic fibrosis (CF) patients. We recently developed an in vitro model of a mixed biofilm associating Af and Sm in RPMI + FBS medium at 37°C for 24 h and discovered an antibiosis effect of Sm ATCC 13637 on Af ATCC 13073-GFP strain (1). The bacteria inhibited the fungal growth and induced an increase of fungal cell wall thickness, which led to abnormal mycelium with highly branched hyphae. The aim of the present study was to assess this antibiosis effect of various Sm strains on different Af strains. Methods: Firstly, the effect of Sm ATCC 13637 was assess on 8 different Af originated from human, animals and environment. Secondly, the effect of 8 Sm strains from different origins (human, animal and hospital environment) and genogroups (MLST profiles) was evaluated on Af ATCC 13073-GFP strain. Fungal and bacterial inocula (105 conidia/mL and 106 cells/mL, respectively) were simultaneously inoculated on polystyrene supports in RPMI + FBS medium at 37°C or 25°C for 16-24 h. The modifications of Af in absence (fungal biofilm) or presence (mixed biofilm) of bacteria were assessed. The inhibition of fungal growth was analysed by qPCR method, biofilm thickness and Af phenotype via CLSM and the fungal cell wall modifications by TEM analysis. Results: All the 8 Af strains tested were able to adhere to polystyrene and form single and mixed biofilm with Sm ATCC 13637. In mixed biofilms, all the Af strains tested presented an inhibition of biofilm biomass and of fungal growth, highly branched hyphae and an increase of fungal cell wall thickness. In contrast, the 8 Sm strains tested were not able to form mixed biofilm with Af ATCC 13073-GFP in the conditions of biofilm formation (37°C, in RPMI + FBS medium). Only strains belonging to genogroup 6 (from human and dog) were able to grow at 37°C and induce an increase of fungal cell wall thickness and an inhibition of fungal growth. The others Sm strains (from environment and horse) were only able to grow at 25°C. These strains didn’t induce antibiosis effect on Af at 37°C, but at 25°C the bacteria were able to grow in mixed biofilm and to have the same antibiosis effect on Af. Conclusion: All the A. fumigatus strains seem to be susceptible to the antibiosis effect of S. maltophilia, but this effect seems to be concentration-dependent of Sm, and may be related to Sm fitness. All the strains of Sm are able to induce inhibition of fungal growth and an increase of fungal cell wall thickness depending of culture conditions. In this study, only Sm strains form genogroup 6, originated from human pathologies (cystic fibrosis or deep infection), can grow at 37°C and induce antibiosis effect on Af at this temperature. After this strain-evaluation, we will use our mixed biofilm model to evaluate efficiency of different bacterial and antifungal agents. 1. Melloul E et al. PLoS One. 2016.21;11(11):e0166325.
Full conference title:
The 8th Advances Against Aspergillus, Lisbon Conference Center, Lisbon, Portugal
- AAA 8th (2018)