Previously described methods to study the motility of Helicobacter pylori (H. pylori) in response to chemical gradients (chemotaxis) are subject to limitations such as false positives, long assay times, and low sensitivity. While automated tracking of individual cells within the well-defined environments produced in microfluidic devices has been successfully applied to study other bacteria, the combination has not previously been reported for H. pylori. Steeper concentration gradients established in our microfluidic device help overcomes some difficulties in fitting the model given in, which explains how a given chemoeffector biases the random walk. Results collected for E. coli help validate performance of the microfluidics, data analysis, since chemotaxis in E. coli is well understood.

Main results include application of the above microfluidic and computer model to study H. pylori response to the known attractant urea, and the known repellent bile acid deoxycholic acid. While it has been found that H. pylori growth is inhibited by capsaicin, it was previously unknown whether capsaicin is an attractant, repellent or otherwise impacts behaviour.

Results help to address an apparent conflict between previous in vitro tests, which suggest that capsaicin inhibits H. pylori growth, and epidemiological studies which link higher capsaicin consumption with morbidity. Analysis of the fitted model suggests whether or not the H. pylori chemotactic response adapts to a background concentration. Evidence for adaptation lends support to the hypothesis that CheV are responsible for this behaviour in H. pylori.

Understanding the Adhesion Kinetics of Biofilms on Food Contact Surfaces using Nanotechnology

Biofouling on food industry equipment leads to economic losses from corrosion, equipment impairment, and reduced heat transfer efficiency.  Common food contact surfaces such as stainless steel are robust; however, they can encourage bacterial attachment and subsequent biofilm formation.  Attachment of bacteria on food contact surfaces is the first step towards biofilm development.  The overall goal of this research is to better understand the interaction between the microorganisms, Pseudomonas aeruginosa and methicillin-resistant Staphylococcus aureus (MRSA), and substrates on which these microorganisms adhere.  The relation between the bacterial cell surface electrokinetic potential at the nanoscale, and the ability of these microorganisms to attach to stainless steel and gold surfaces was assessed through Atomic Force Microscopy and Kelvin Probe Force Microscopy.

AFM results showed that no microbial attachment occurred after 3 hours of incubation on non-functionalized surfaces while poly-L-lysine functionalized surfaces showed microbial attachment after 30 minutes.  Poly-L-lysine is a common food preservative and can act as a microbial attachment factor depending on bond orientation.  KPFM data revealed positive surface potentials on stainless steel compared to negative surface charges on gold surfaces.  Pseudomonas aeruginosa showed larger membrane potentials than MRSA, with MRSA showing noticeably different membrane potentials between gold and stainless steel surfaces.

Antimicrobial Efficacy of Soy Isoflavones against Listeria Monocytogenes

Food-borne pathogenic biofilms in food processing and manufacturing industries have led to food spoilage, bio fouling, and food-borne illnesses. Antimicrobial coatings and films serve as a barrier against bacterial contamination. Chemical or synthetic antimicrobial coatings are widely used today which are not necessarily safe. The demand for antimicrobial coatings in food applications is estimated to reach USD 2.7 billion in the year 2018. With an increased demand for antimicrobial coatings and a need to effectively inhibit microbial biofilms, new coatings need to be developed. The unique properties of soy isoflavones such as biodegradability, biocompatibility and edibility over artificial polymer or chemical based coatings could make it an ideal antimicrobial agent to prevent bacterial growth in a variety of environments.  This research explores the effectiveness of soy isoflavones for use in the food industry by assessing their antimicrobial efficacy against Listeria monocytogenes using microtiter plate assay (MPA) and imaging techniques. The end results of this research would help the food industry to develop natural, novel, eco-friendly, edible, biocompatible, biodegradable, multi-purpose antimicrobial coatings or agents to inhibit the growth of microbial biofilm and provide food safety to the consumers. It would also result in a significant contribution to Ontarian soy growers by increasing their opportunities and adding value to their crop. It would be very significant to the Government in reducing the cost spent on health sector and help in the mission of providing “health and wellness” to the citizens of Canada.

Cross contamination of food by pathogens via surfaces increases the risk of the propagation of infectious diseases. E.Coli and Listeria species are the predominant bacterium that causes fouling on food processing surfaces, chutes, cutting tables, tube systems, pipes and conveyor belts. The knowledge of the ability of the material surface for bacterial colonization is essential for selecting and designing surfaces for food processing. Characterization and optimization of surface pre-treatment with anti-microbial coatings will prevent the biofilm formation, and thereby will ensure food safety. Silver zeolite (SZ) acts as a smart surface coating. Upon contact with moisture, silver and highly reactive oxygen ions are released from the crystalline structure. The silver ions interact with the bacteria’s proteins and DNA. The oxygen acts as a free radical oxidizing components within the bacteria. The objectives of this project are (i) To investigate the interaction of the food pathogenic bacteria with various surfaces, and (ii) To assess the rate of antimicrobial activity of selected disinfectants against the pathogenic bacteria.

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Bionanotechnology Laboratory
Suresh Neethirajan

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University of Guelph
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Lab: THRN 2133 BioNano Lab

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