Adaptive responses of salmonella enterica serovar enteritidis ATCC 4931 biofilms to nutrient laminar flow and benzalkonium chloride treatment
Illathu, Anilkumar Mangalappalli
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Salmonella enterica serovar Enteritidis is an important biofilm-forming food-borne pathogen. This study examined the adaptive responses of Salmonella serovar Enteritidis biofilms to different environmental conditions such as flow velocity and benzalkonium chloride (BC) treatment. The influence of a 10-fold difference in nutrient laminar flow velocity on the dynamics of biofilm formation and protein expression profiles was compared. The mode of development and architecture of low-flow and high-flow biofilms were distinct. Exopolymer composition of the two biofilms was also different. However, no major shift in protein expression was seen between the biofilms, nor were there any stress response proteins involved. The biofilms altered their architecture in response to flow, presumably assuming a structure that minimized overall biofilm stress. An empirically-determined shear-inducing flow was applied on high-flow biofilms, fractionating the biofilms into shearable and non-shearable regions. Length:width indices of cells from the two biofilm regions, as well as planktonic cells from biofilm effluent and continuous culture were determined to be 3.2, 2.3, 2.2, and 1.7, respectively. Expression of proteins involved in cold-shock response, adaptation, and broad regulatory functions in the shearable region, and expression of protein involved in heat-shock response and chaperonin function in the non-shearable region indicated that the physiological status of cells in two biofilm regions was also distinct. The development of biofilm adaptive resistance to BC was then examined. Adapted biofilms survived a lethal BC challenge and re-grew, whereas unadapted biofilms did not. Proteins up-regulated following adaptation included those involved in energy metabolism, amino acid and protein biosynthesis, nutrient-transportation, adaptation, detoxification, and 1,2-propanediol degradation. A putative universal stress protein was also up-regulated. Cold-shock response, stress response, and detoxification are suggested to play roles in adaptive resistance to BC. Functional differences in adaptive response and survival of plankonic and biofilm cells adapted to BC were also studied. The proportion of BC-adapted biofilm cells that survived a lethal BC exposure and heat-shock was significantly higher than that of BC-adapted planktonic cells. Enhanced biofilm-specific up-regulation of various proteins, coupled with alterations in cell surface roughness and shift in fatty acid composition are proposed to function in the enhanced survival of BC-adapted biofilm cells, relative to BC-adapted planktonic cells.It is concluded that biofilms adapt to the stress conditions by means of community, cellular, and sub-cellular level responses. These adaptive responses help the biofilms to enhance their ability for survival in the nature, especially those formed in critical environments such as healthcare facilities, the food industry, and households.
DegreeDoctor of Philosophy (Ph.D.)
DepartmentApplied Microbiology and Food Science
ProgramApplied Microbiology and Food Science
SupervisorKorber, Darren R.
CommitteeTanaka, Takuji; Shand, Phyllis J.; McMullen, Lynn M.; Lawrence, John R.; Van Kessel, Andrew G.
Salmonella serovar Enteritidis
Nutrient laminar flow