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Title: Comparative genomics of two super-shedder isolates of Escherichia coli O157:H7

item KATANI, ROBAB - Pennsylvania State University
item COTE, REBECCA - Pennsylvania State University
item Kudva, Indira
item DEBROY, CHITRITA - Pennsylvania State University
item Arthur, Terrance
item KAPUR, VIVEK - Pennsylvania State University

Submitted to: PLOS ONE
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 7/27/2017
Publication Date: 8/10/2017
Citation: Katani, R., Cote, R., Kudva, I.T., DebRoy, C., Arthur, T.M., Kapur, V. 2017. Comparative genomics of two super-shedder isolates of Escherichia coli O157:H7. PLoS One. 12(8):e0182940. https://doi:10.1371/journal.pone.0182940.

Interpretive Summary: Shiga toxin-producing Escherichia coli O157:H7 (O157) are foodborne pathogens that can cause severe disease in humans including diarrhea, bloody diarrhea that may, in some cases, lead to kidney failure and death. Cattle carry O157 in their intestines without any disease and shed these bacteria in their feces. Hence, O157-containing cattle feces are the main source of food and environmental contamination. Some cattle shed O157 in high numbers in their feces and have been termed "Super-shedders". Super-shedding cattle can easily disseminate O157 within large herds. Hence, it is important to control /prevent O157 colonization of cattle. To derive methods to control O157, the mechanisms of attachment used by these bacteria to colonize the cattle intestinal tract, and the phenomenon of super-shedding are being studied. Here, we specifically studied two super-shed O157 strains and compared them with other previously characterized O157 strains. We have found that super-shed O157 have unique, recently acquired, genetic features that could serve as targets for the development of O157 blocking therapies for use in cattle.

Technical Abstract: Shiga toxin-producing Escherichia coli O157:H7 (O157) are zoonotic foodborne pathogens and of major public health concern that cause considerable intestinal and extra-intestinal illnesses in humans. O157 colonize the recto-anal junction (RAJ) of asymptomatic cattle who shed the bacterium into the environment through fecal matter. A small subset of cattle, termed super-shedders (SS), excrete O157 at a rate (greater than or equal to 104 CFU/g of feces) that is several orders of magnitude greater than other colonized cattle and play a major role in the prevalence and transmission of O157. To better understand microbial factors contributing to super-shedding, we have recently sequenced two SS isolates, SS17 (GenBank accession no. CP008805) and SS52 (GenBank accession no. CP010304) and shown that SS isolates display a distinctive strongly adherent phenotype on bovine rectal squamous epithelial cells. Here we present a detailed comparative genomics analysis of SS17 and SS52 with other previously characterized O157 strains (EC4115, EDL933, Sakai, TW14359). The results highlight specific polymorphisms and genomic features shared amongst SS strains, and reveal several SNPs that are shared amongst SS isolates, including in genes involved in motility, adherence, and metabolism. Finally, our analyses reveal distinctive patterns of distribution of phage-associated genes amongst the two SS and other isolates. Together, the results of our comparative genomics studies suggest that while SS17 and SS52 share genomic features with other lineage I/II isolates, they likely have distinct recent evolutionary histories. Future comparative and functional genomic studies are needed to decipher the precise molecular basis for super shedding in O157.