E&E PhD Exit Webinar: The ecological niche of human-associated Escherichia coli (E. coli)

Extra-intestinal pathogenic Escherichia coli (ExPEC) strains are responsible for the majority of extra-intestinal infections in humans, including urinary tract infections, neonatal meningitis, and bacteraemia. The extra-intestinal infections caused by ExPEC strains result in increasing number of deaths and increasing medical costs. Sequence type (ST)73, ST95, and ST131 are well-known as predominant ExPEC lineages. They have been observed to have distinct ecological niches, but the knowledge about the differences among these three STs remains little. The purpose of this study was to investigate phenotypic and genotypic characteristics of strains belonging to these lineages by performing numerous phenotypic experiments and analysing their pan-genome and whole genome contents. The results of this study suggested that there was no difference among ST73, ST95, and ST131 in NLRP3 inflammasome activation, expression of type 1 fimbriae, and biofilm formation. Additionally, strains from these STs exhibited the sensitivity to bile salts and their ability to form biofilm significantly reduced in the presence of bile salts at 24oC. This study revealed that ST131 strains were distinguished from ST73 and ST95 strains by exhibiting the highest ability to tolerate to acidity, to metabolise a variety of substrates, to resist to many types of antibiotics. Furthermore, ST131 strains were more sensitive to being killed by bacteriocins or bacteriophages than those from other STs. Unlike ST95 and ST131 strains, ST73 strains displayed their strengths in invading into mammalian cells, producing bacteriocins, resisting to heat stress, and utilising some substrates. In terms of ST95 strains, it was observed that they had the lowest metabolic activity, but they had the highest number of intact prophages in their genome, and they showed the highest resistance to some inhibition factors such as bacteriocins and bacteriophages. Combining all results of phenotype and genotype of strains from ST73, ST95, and ST131, this study convinced that there was an exclusive competition, resulting in very distinguished ecological niches among these three STs. Particularly, in the rich-nutrient environments, ST131 strains would outcompete other STs strains and prevent the competitors from using available nutrients. However, ST73 and ST95 strains might defeat ST131 strains in the low-nutrient environments by producing bacteriocins and bacteriophages, respectively. Similarly, ST73 strains would prevail in the competition with ST95 strains to gain access into the availability of nutrients. However, in the low-nutrient environments, ST95 strains might be the winner in the competition with ST73 strains due to their resistance to bacteriocins and the release of prophages from their cells. Besides that, the intestinal tract is known as original reservoir of ExPEC strains. However, poultry meat has been suggested to be a potential reservoir of these strains, who might deal with high temperature stress during cooking preparation. This study observed the better resistance to heat stress of ST73 strains in comparison with strains from ST95 and ST131, supporting the frequent occurrence of ST73 strains in poultry products and the potential transmission of the infections from these products to humans. Additionally, ST131 strains responsible for the multidrug resistant infections had the sensitivity to bacteriocins and bacteriophages that might lead to the promising treatments of these infections by replacing traditional antibiotics with bacteriocins or bacteriophages.