Efficacy of conventional and novel antimicrobial treatments on the inactivation of desiccated cells and biofilms of Salmonella
Creators: Dhaliwal, Harleen Kaur
Publisher: name: University of Alberta Library
Year: 2024

<p>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. 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.<br>
Salmonella is responsible for numerous foodborne outbreaks associated with low-water activity (aw) 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, aw, and strain type on the desiccation and subsequent thermal survival of Salmonella. In the first study, three low-aw foods (pet food, burger binder and skim milk powder) were wet inoculated with the different Salmonella spp. and desiccated to aw 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 aw change at the treatment temperature, on its survival. Furthermore, the water sorption isotherms of the selected low-aw foods were developed to relate the thermal survival of Salmonella to the aw change at 70 °C. Sorption isotherms displayed a significant increase in the aw of the pet foods as compared to burger binder and skim milk powder. However, the observed Salmonella thermal inactivation kinetics demonstrated the role of a complex interaction between the strain type, aw, and food composition rather than being affected by a single parameter.<br>
The low-aw 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 can vary based on its cellular state. In the second study, Salmonella Enteritidis FUA1946 was inoculated on 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-activated 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.<br>
Salmonella uses biofilm formation as a mechanism for survival. Generally, true biofilms are formed inside close infrastructures like 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 on 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.<br>
This PhD thesis research demonstrated the effectiveness of various conventional and novel disinfection technologies in the inactivation of Salmonella in low-aw environments and in biofilms. The knowledge gained in this research would help in the appropriate selection of disinfection protocols for effective Salmonella control from the food industry.</p>