UBC Theses and Dissertations
Novel approaches to studying foodborne pathogen biofilms and insoluble layers at an air-liquid interface Bogan, Abner L.
In the context of food safety and public health, biofilm research is of great importance for mitigating the virulence of food-borne pathogens in food processing environments. To supplement the widely used biochemical-based methods for biofilm characterization, we introduce three non-traditional imaging assays to assess biofilm robustness at the solid-liquid and air-liquid interfaces in Pseduomonas aeruginosa, Acinetobacter baumanii, Listeria monocytogenes and Salmonella enterica. These assays are carried out either using standard microwell plates contained in a custom chamber or a modified pendant droplet apparatus, both of which could be easily recreated in other laboratories. Despite indications of a surface-attached, air-liquid biofilm (at the meniscus in a microwell) with traditional crystal violet staining for all strains, our assays showed that only Pseudomonas aeruginosa and Acinetobacter baumanii were able to form biofilms on particles (of the same material as the well) at the air-liquid interface. In a pendant droplet, all strains except for Listeria were shown to form air-liquid biofilms through an end-point droplet compression and expansion test, though only Pseudomonas aeruginosa formed highly elastic biofilm layers. The results from the pendant-droplet assay were supplemented by a simple, yet novel in-situ, floating-biofilm reflection-test which showed that only Pseudomonas aeruginosa formed pellicles that significantly alter visible light reflection from the liquid surface. As a second topic in this thesis, we also develop the workings for a dip-coating method to study the thermodynamic behavior of surface-associated insoluble monolayers at an air-liquid interface of a pendant droplet. The pendant droplet serves as a model system to analyze insoluble monolayers at fluid-fluid interfaces that are small and curved in nature. Examples of such interfaces in biological systems include vesicles, lung alveoli and other colloids. As biofilms at air-liquid interfaces are much less studied than solid-liquid biofilms, this simple dip-coating method may also assist in micromechanical analysis of air-liquid biofilms for future biophysical research.
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