One-step soft agar enrichment and isolation of human lung bacteria inhibiting the germination of Aspergillus spp. conidia

Author:

Fabio Palmieri (CH)

Abstract:

Background:
Given the unprecedented rise in antifungal resistance worldwide, alternative treatments for fungal infections are urgently needed. The remarkable ability of Aspergillus spp., to effectively colonize and grow in a diverse range of environmental settings, from a human host to compost piles, can be associated to their ability to manipulate the local conditions. For instance, A. niger, is known to excrete large quantities of oxalic acid to acidify its microenvironment. This mechanism can also occur during lung infection as the accumulation of calcium oxalate crystals in the lungs has been observed during Aspergillus infection. The accumulation of calcium oxalate crystals results not only on acidification, but also in the mechanical damage of the epithelial cells. In vitro, Cupriavidus oxalaticus has been shown to degrade oxalic acid, thereby increasing pH locally and controlling A. niger growth. The same mechanism could be used to control fungal growth in the lung via a mechanism called environmental interference. The aim of this study was to demonstrate the potential of this mechanism as an innovative biocontrol strategy in a translational setting.

Methods:
The biocontrol potential of C. oxalaticus on the development of A. niger was assessed across complementary experimental models ranging from in vitro AXLung-on-chip system pre-seeded with human-derived immortalized alveolar epithelial cells (AXiAEC), all the way to in vivo models using Galleria mellonella larvae and murine adult immunocompromised BalbC/J mice. To do so, infection with A. niger, colonization with C. oxalaticus, or a combination of both was performed in all of the above-mentioned experimental models. Microenvironmental factors such as pH, and calcium concentrations, were measured. Conidia germination and hyphal growth of A. niger was assessed through microscopy. Transepithelial electrical resistance and cell morphology were assessed in the in vitro cell culture models.

Results:
In vitro, exposure of AXiAEC to C. oxalaticus altered cell morphology and enhanced barrier integrity. Infection with A. niger modified pH, Ca2+ and oxalic acid concentrations and led to impaired barrier integrity, where subsequent co-exposure with C. oxalaticus rescued this effect. Interestingly, this biocontrol mechanism could not be demonstrated in vivo in G. mellonella larvae as the C. oxalaticus inoculation was lethal. In the preclinical murine model, we optimized an A. niger infection dose leading to hyphal formation in the lungs but with minimal distress for the animals. Colonization with C. oxalaticus led to immune priming with negligible airway inflammation, and analyses of the confrontation exposures are currently ongoing.

Conclusions:
We successfully demonstrated the potential of using a biocontrol strategy based on environmental interference in a translational setting in the context of Aspergillus infection. This is the first time that biocontrol bacteria are used to contain respiratory fungal infection.

Abstract Number: 54

Conference Year: 2024

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