Phenotypic and genomic comparison of three human outbreak and one cattle-associated Shiga toxin-producing O157:H7.

UNLABELLED

O157:H7-adulterated food products are associated with disease outbreaks in humans. Although cattle feces are a source for O157:H7 contamination, it is unclear if human-associated outbreak isolates differentially colonize and shed in the feces of cattle from that of non-outbreak isolates. It is also unclear if phenotypes, such as biofilm formation, cell attachment, or toxin production, differentiate environmental O157:H7 isolates from those associated with human illness. The objective of this study was to compare the genotypes and phenotypes of a diverse set of O157:H7 isolates, with the intent of identifying differences that could inform cattle colonization and fecal shedding, along with virulence potential in humans. Isolates differed in attachment phenotypes on human Caco-2 cells and bovine-derived recto-anal junction squamous epithelial cells, with curli having a strong impact on attachment to the human-derived cell line. The prototypical O157 isolate EDL933 had the greatest expression of the adhesin gene , yet it had decreased expression of the virulence genes , , and compared the lineage I/II isolates RM6067W and/or FRIK1989. Strong or weak biofilm production was not associated with significant differences in cattle colonization or shedding, suggesting biofilms may not play a major role in cattle colonization. No significant differences in cattle colonization and fecal shedding were detected, despite genomic and phenotypic differences. The outbreak isolate associated with the greatest incidence of hemolytic uremic syndrome, RM6067W, induced the greatest Vero cell cytotoxicity and had the greatest gene expression.

IMPORTANCE

Foodborne illness has major impacts on global health and imposes financial hardships on food industries. serotype O157:H7 is associated with foodborne illness. Cattle feces are a source of O157:H7, and routine surveillance has led to an abundance of O157:H7 genomic data. The relationship between O157:H7 genome and phenotype is not clearly discerned for cattle colonization/shedding and improved understanding could lead to additional strategies to limit O157:H7 in the food chain. The goal of the research was to evaluate genomic and phenotypic attributes of O157:H7 associated with cattle colonization and shedding, environmental persistence, and human illness. Our results indicate variations in biofilm formation and cellular adherence was not associated with differences in cattle colonization or shedding. Overall, processes involved in cattle colonization and various phenotypes in relation to genotype are complex and remain not well understood.