2:00 pm - 3:00 pm
Event details: A graduate exam seminar is a presentation of the student’s final research project for their degree.
This is an ALES MSc Final Exam Seminar by Zhiying Wang. This seminar is open to the general public to attend.
Zoom meeting: https://ualberta-ca.zoom.us/j/99931984703
Stress resistance of Enterobacteriaceae in food and water
PhD with Dr. Michael Gaenzle
Bacterial species in the order Enterobacterales populate diverse ecological niches including soil, water, nematodes, insects, plants, and vertebrates. Many Enterobacteriaceae temporarily inhabit the intestine of vertebrate hosts but also survive and thrive in extra-intestinal habitats to transit between host individuals. These species acquire stress resistance genes to overcome dispersal limitations and environmental stresses; these stress resistances also challenge pathogen control in the food industry and hospitals. The research described in this thesis aimed to investigate the role of stress resistance genes in host adaptation and their impact on food safety and public health. Samples from Daqu fermentation, wastewater, and fresh water contained Enterobacteriaceae that harbored a genomic island termed the transmissible locus of stress tolerance (tLST), which confers extreme heat resistance. Functional genomics demonstrated that the tLST also confers resistance to chlorine and other oxidizing chemicals, and identified that 7 proteins encoded by the tLST are necessary for heat or chlorine resistance. Comparative genomics demonstrated that the tLST is particularly present in those Enterobacteriaceae that occur in plant-associated habitats as well in the intestine of vertebrates. The frequency of the tLST in clinical isolates of Klebsiella and Cronobacter species suggests that tLST-mediated resistance may contribute to their persistence in hospitals. The function of the genomic island was also characterized by competition experiments of isogenic tLST-positive and tLST-negative strains. These demonstrated that the fitness gain during lethal challenge with chlorine is associated with a substantial fitness cost in the absence of chemical or physical stressors.
The presence of tLST excluded virulence factors of several pathogens including Shigella, Shiga-toxin producing E. coli, uropathogenic E. coli, and Salmonella. To determine whether the accessory genome of Salmonella also includes genes that contribute to stress resistance, comparative and functional genomic analyses were used to identify genes related to the resistance of Salmonella to desiccation and dry heat. Of the 289 genes that were differentially distributed in resistant and sensitive strains of Salmonella, 7 genes were confirmed to contribute to dry-heat resistance or high-pressure resistance by expression in sensitive strains. Taken together, this study improves the understanding of the contribution of genetic determinants to stress resistance and host adaptation in Enterobacteriaceae, which allow improved control of pathogenic Enterobacteriaceae.