Harleen Kaur Dhaliwal | ALES Graduate Seminar

A graduate exam seminar is a presentation of the student’s final research project for their degree.
This is an ALES PhD Final Exam Seminar by Harleen Kaur Dhaliwal. This seminar is open to the general public to attend, either in-person or online:

https://ualberta-ca.zoom.us/j/97885693924?pwd=cXFpZk9KWm9LN3RqeEEvUlArVkRJUT09
Meeting ID: 978 8569 3924 | Passcode: 934916

Thesis Topic: Efficacy of conventional and novel antimicrobial treatments on the inactivation of desiccated cells and biofilms of Salmonella

PhD with Dr. Roopesh Syamaladevi.

Seminar Abstract:

Repeated isolation of Salmonella from the dry and wet environments of the food industry poses a significant concern to human health. It is crucial to understand the influence of the various environmental conditions on Salmonella’s survival against disinfection treatments. The overall objective of this research was to evaluate the efficacy of various conventional and novel disinfection approaches in the inactivation of Salmonella under diverse conditions of the food industry.

Salmonella is responsible for numerous foodborne outbreaks associated with low-water activity (a_w) foods. Thermal treatment is widely used to minimize the risk of Salmonella from such foods. An increase in the thermal resistance of Salmonella post-desiccation stress has been well documented. It is important to investigate the potential effect of food composition, a_w, and strain type on the desiccation and subsequent thermal survival of Salmonella. Three low-a_w foods (pet food, burger binder and skim milk powder) were wet inoculated with the different Salmonella spp. and desiccated to a_w of 0.33 and 0.75. The thermal inactivation kinetics of Salmonella spp. obtained following an isothermal treatment at 70 °C, demonstrated an interactive effect of the food composition, and a_w change at the treatment temperature, on its survival. Furthermore, the water sorption isotherms of the selected low-a_w foods were developed to relate the thermal survival of Salmonella to the a_w change at 70 °C. Sorption isotherms displayed a significant increase in the a_w of the pet foods as compared to burger binder and skim milk powder. However, the observed Salmonella thermal inactivation kinetics demonstrated the role of complex interaction between the strain type, a_w, and food composition rather than being affected by a single parameter.

The low-a_w food contamination can also occur via contaminated food contact surfaces. Conventional disinfectants such as oxidizers (hydrogen peroxide, peracetic acid), dry heat and membrane-acting quaternary ammonium compounds are frequently used for the disinfection of food contact surfaces. However, Salmonella survival in response to the disinfection process will vary based on its cellular state. In the second study, Salmonella Enteritidis FUA1946 was inoculated on the stainless steel under different desiccation conditions (air drying and air drying followed by equilibration to a relative humidity of 33%). Their inactivation was assessed using conventional and novel (plasma activate water bubbles, plasma-activated hydrogen peroxide water bubbles) disinfectants. The results demonstrated a significant effect of the concentration, treatment temperature, and exposure time on the inactivation of the desiccated bacteria. The desiccation method significantly influenced the disinfection survival of Salmonella. Furthermore, the efficacy of plasma-activated water bubbles, recirculated under different hold and flow times was evaluated against the air-dried and equilibrated Salmonella on stainless steel surfaces. Increasing the plasma flow time significantly enhanced the inactivation of the surface-attached bacteria.

Salmonella uses biofilm formation as a mechanism for survival. Generally, true biofilms are formed inside close infrastructures such as pipelines. Chemical disinfectants are used for the disinfection of the drinker lines. However, their persistent use can form hazardous by-products. In the third study, the disinfection effectiveness of plasma-activated water bubbles (PAWB) under different hydrodynamic variations against the mixed species biofilms was evaluated. A benchtop pipeline model simulating the industrial pipelines was built. Salmonella ATCC13311 and Aeromonas australiensis 03-09 were used to form mixed-species biofilms in the inner surfaces of the PVC pipes. The effectiveness of laminar (Re 1000), transitional (Re 2500) and turbulent (Re 4000) flow regimes in the inactivation of mixed-species biofilms was examined, followed by an investigation into the effect of treatment time on the biofilm inactivation. In the third set of experiments, the effectiveness of the constant volume flow rate was evaluated against the biofilm adhered to the pipe walls. PAWB recirculation under high Reynold’s number resulted in a greater inactivation of the biofilms. The interactive effect of the PAWB reactive species, the volume of PAWB circulated, and the shear stress generated using the different flow regimes significantly improved the inactivation of the biofilms from the pipe walls. Moreover, bacteria in the bulk water was highly susceptible to the action of PAWB.

The research demonstrated the effectiveness of various conventional and novel disinfection technologies in the inactivation of Salmonella in low-a_w environments and in biofilms. The knowledge gained in this research would help in the appropriate selection of the disinfection protocols for effective Salmonella control from the food industry.