Phenotypic and genomic comparison of human outbreak and cattle-associated Shiga toxin-producing Escherichia coli O157:H7

Abstract

Escherichia coli O157:H7 (O157)-adulterated food products, including beef and produce, are associated with disease outbreaks in humans. Although cattle feces are a source for the contamination, it is unclear if diverse O157 human-associated outbreak isolates expressing a specific virulence phenotype can colonize and shed in the feces of cattle at a quantitatively similar levels to non-outbreak isolates. It is also unclear if other phenotypes, such as biofilm, cell attachment, and toxin production, differentiate environmental O157 isolates from O157 isolates associated with human illness. Genomic profiling of O157 isolates acquired through routine surveillance can inform if the isolates encode virulence genes associated with human disease, but many genotype-phenotype relationships remain unclear for O157. Therefore, the objective of this study was to compare a diverse set of O157 isolates, with the intent of identifying potential genotypic differences that could inform phenotypes such as cattle colonization and fecal shedding, in vitro cell attachment, biofilm production, and Shiga toxin production. In addition, the relationship between phenotypes and potential for foodborne illness as it relates to genomic virulence traits was explored. No significant differences in cattle colonization and fecal shedding were detected for the tested isolates, despite broad genomic differences. In addition, the in vitro phenotypic differences noted in biofilm and cell attachment did not associate with one LSPA-6 lineage compared to another. Overall, no differences in cattle shedding were observed, yet variations in genotype and phenotype were identified indicating further work is warranted to better understand the relationship between O157 genome and virulence. ImportanceFoodborne illness has a major impact on the health and wellbeing of the global population, besides creating substantial financial hardships for industry. While many bacteria and viruses are implicated in foodborne illness, Escherichia coli serotype O157:H7 (O157) is a common food adulterant that can cause human disease and food recalls. Cattle feces are a significant source of food-adulterating O157. A greater understanding of O157 genetics and its relation to phenotype is needed to develop mitigation strategies to limit spread of O157 into the food chain. The goal of the research was to identify O157 genomic and phenotypic attributes of O157 associated with cattle colonization and fecal shedding along with other factors involved in environmental persistence and illness in humans. It was observed that variations in biofilm formation and in vitro cellular adherence did not associate with enhanced cattle colonization or fecal shedding, indicating that the processes involved in cattle colonization are complex and not well understood.