A novel nrontier in food safety :meeting the evolutionary challenges posed by Escherichia coli

Abstract

Escherichia coli (E. coli) is an enterobacteria that inhabits the gastrointestinal tract of warm-blooded animals and the environment in general. Nine of its serotypes are frequently associated with foodborne illnesses and can lead to intra- and extraintestinal infections in humans, and in some cases to death. In the food chain, heat treatments are one of the main alternatives to combat the bacteria. However, with a genome in constant evolution, E. coli has undergone changes in its genetic machinery over the years, which has contributed to its ability to overcome various challenges imposed by humans. In this way, this thesis aimed to phenotypically characterize pathogenic E. coli isolated from food, animals and humans from different parts of the world, in relation to their ability to overcome ecological pressures, in an attempt to understand the role of the bacteria's genetic machinery in this context. In order to characterize the bacteria's heat resistance phenotype, E. coli strains isolated from animal-based food (beef and pasteurized milk) were exposed to treatments of 60 and 71°C. Then, the strains that showed a moderate and high heat resistance were selected for whole genome sequencing in order to identify genes present in the heat resistance island called transmissible locus of stress tolerance (tLST). Through genome sequencing we carried out a prevalence of tLST in E. coli from across Brazil. Afterwards, genome sequencing was also carried out on E. coli isolated from chicken from supermarkets in Peru, in order to genetically characterize the antimicrobial resistance of the bacteria.Furthermore, a collection of E. coli from humans and other diverse animals, isolated from different parts of the world, and stored in the laboratory located in the department of microbiology and immunology at the University of Texas Medical Branch in Galveston, Texas, United States, were used to identify potential proteins related to the production of biofilm by the bacteria when in the presence of bile salt. Based on all the data on the resistance phenotype and genotype of E. coli from various sources, some of these strains, isolated from animal products, were selected and subjected to survival challenges using two promising innovative non-thermal technologies: ultraviolet light-emitting diodes (UVC-LED) and ultrasound (US). Using these results, a final study was conducted using infrared (FT-IR) in order to understand the biomolecular behavior of the bacteria when exposed to thermal (60°C) and non-thermal (UVC-LED and US) conditions. The results of this thesis demonstrated the high adaptability of E. coli isolated from diverse sources to overcome extrinsic (heat, non-thermal technologies) and intrinsic host (bile salt) environmental stresses. The genetic machinery of the bacteria investigated through genome sequencing data showed the presence of numerous genes responsible for resistance, persistence and virulence. The results of this work will be instrumental in developing new approaches capable of eliminating the E. coli.