UBC Theses and Dissertations
Identification of natural compounds to quench quorum sensing in Campylobacter jejuni for the reduction of biofilm formation Li, Shenmiao
Quorum sensing is a process of bacterial intercellular communication that relies on the production and perception of chemical signals called autoinducers. Via quorum sensing, bacteria can modulate a range of behaviours in response to the change of population density for better fitness. Quorum sensing mediated biofilm formation is a vital survival strategy for many bacteria. At a high population density, bacteria can aggregate and attach to a surface by producing and secreting extracellular polymeric substances (EPS). The surrounding EPS protects the encased cells from the unfavourable conditions. Campylobacter jejuni is a major bacterial cause of human diarrhoeal diseases worldwide. Despite its sensitivity to environmental stresses, C. jejuni ubiquitously distributes throughout the poultry production chain. Autoinducer-2 (AI-2) mediated biofilm formation is known to be critical to the environmental survival of C. jejuni. C. jejuni possesses LuxS, the enzyme involved in the production of AI-2. In this dissertation, two natural fatty acids, namely decanoic acid and lauric acid, were identified as AI-2 inhibitors of C. jejuni. Decanoic acid and lauric acid at 100 ppm inhibited ~90% AI-2 activity of C. jejuni without inactivation of the bacterial cells. Anti-biofilm effect of decanoic acid and lauric acid was investigated. C. jejuni culture was incubated with or without the treatment by fatty acids for 72 h. Biofilm biomass was determined by crystal violet assay, and the numbers of viable planktonic and biofilm-associated cells were separately determined by the conventional plating assay. Except one C. jejuni strain increased biofilm biomass at the treatment groups, the fatty acids reduced 10-50% of the biofilm biomass in the other strains. Lauric acid at 100 ppm achieved ~3-log and ~2-log reduction of C. jejuni biofilm-associated and planktonic cells, respectively. In addition, both fatty acids effectively reduced C. jejuni motility. This study identified the AI-2 inhibitors of C. jejuni and investigated their inhibitory effect on biofilm formation and motility. The findings of this study can aid in the development of alternative C. jejuni control strategies.
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