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Latchman, Someshwar Ravnit

University of British Columbia

Biofilms are microorganism aggregates embedded in extracellular polysaccharide that form a complex three-dimensional structure. Biofilm formation occurs in multiple food processing systems, and in some cases microorganisms within biofilms enter into a state of dormancy called the viable but nonculturable (VBNC) state where they are still metabolically active but are not detectable using standard culturing techniques. As such, biofilms are a major concern for public food safety and have been implicated in multiple outbreaks. While biofilms found in nature are multi-species communities, most biofilm research is based on the interactions of biofilms consisting of a single species. This project aimed to evaluate multi-species biofilm formation of Salmonella enterica, Shiga toxin-producing Escherichia coli (STEC) and Pseudomonas spp. in combination and individually. The multi-species biofilms were evaluated both in vitro, and through microscopy. In vitro samples were mixed in equal proportions, depending on single-, dual-, or tri-species biofilm treatment, and evaluated via serial plating on species-specific media. In vitro experiments also consisted of using osmotic (5% NaCl medium), and osmotic plus cold (NaCl + 4°C) stressors to determine species growth in single- and multi-species biofilms and the potential induction of the VBNC state. Pixel analysis on confocal microscopy images of the single- and multi-species biofilms was evaluated through the ImageJ software program. Multi-species biofilms formed by STEC, S. enterica, and Pseudomonas spp. displayed three different interactions: competitive, synergistic, and additive. When exposed to external stressors there was a decrease in the number of cells for all three species with the addition of each stressor. However, Pseudomonas spp. were able to grow better in a cold stress environment and outcompete the other two species. Furthermore, Pseudomonas spp. were involved in all of the competitive and synergistic multi-species biofilm interactions, and were part of multi-species biofilms that exhibited tolerance to stressors. Potential VBNC was induced in some cases and the pixel analysis showed results that were consistent with plate counts under non-stress conditions. Understanding the complex interactions of microbes in biofilms by mimicking natural conditions will prevent potential failures in hygiene and consequently increase food safety.

Text

2022-05-20

Attribution-NonCommercial-NoDerivatives 4.0 International

http://hdl.handle.net/2429/81619

Biology

University of British Columbia

UBCO

http://creativecommons.org/licenses/by-nc-nd/4.0/