Complete genome sequence and adherence characteristics of Escherichia coli O157:H7 isolated from super-shedder cattle

Pathobiology Graduate Student
Johne's Disease Integrated Program Project Assistant
Department of Veterinary and Biomedical Sciences
Penn State University, University Park, PA 16802 USA

Robab Katani1, Rebecca Cote1, Matthew R. Moreau1, Indira T. Kudva2, Maria T. Brandl3, Michelle Q. Carter3, Terry M. Arthur4, Chitrita DebRoy1, Michael M. Mwangi1, Istvan Albert1, Juan Antonio Raygoza Garay1, Lingling Li1, Vivek Kapur1

Shiga toxin-producing Escherichia coli O157:H7 (O157) is a zoonotic foodborne pathogen that causes diarrhea, hemorrhagic colitis and hemolytic uremic syndrome in humans. Cattle are reservoirs for O157 and the pathogen inhabits in the terminal recto- anal junction (RAJ) of the intestinal tract of asymptomatic cattle, and is typically shed at between 10 and 100 CFU/g of feces.

A small subset of cattle, termed "supershedders" (SS), shed O157 at a rate that is several orders of magnitude greater than other colonized cattle (104 CFU/g of feces). Epidemiological studies have indicated that while the number of SS animals on farms is

<10%, they are responsible for 99% of the O157 shed into the environment, and major contributors to the persistence and spread of O157 on the farm and through the food production chain. To better understand the molecular mechanisms that may contribute to super-shedding, we sequenced the complete genome of an isolate of O157 (SS17) recovered from SS cattle. Shotgun sequencing was used to obtain a high quality (>100X coverage) scaffold of the complete genome of SS17, and the genome was closed using a primer walking strategy. The SS17 genome was annotated to identify genes and other genomic features, and comprehensive comparative genomic analyses were performed with previously characterized reference E. coli genomes (EC4115, EDL933, Sakai, TW14359). The results show that the SS17 has an ~5.5Mb genome and carries two plasmids, pO157 and pSS17 of 95kb and 37kb, respectively. Phylogenetic analyses suggested that SS17 is genetically distinct from previously sequenced isolates, and clusters with lineage I/II spinach outbreak isolates (EC4115 and TW14359) as compared to lineage I outbreak isolates (Sakai and EDL933) or the bovine lineage II isolates.

Interestingly, SS17 exhibited unique strong aggregative adherence phenotype on bovine RAJ squamous epithelium (RSE) as compared with reference isolates (EDL933 and 86- 24). Our results suggest that SS isolates are a genetically diverse group of isolates, and SS17 has unique genetic characteristics including novel point mutations in virulence related genes and an unique adherence pattern on host cells that may play a role in the super-shedding phenotype. Further studies that seek to identify the genetic basis for the distinctive adherence phenotype and its contribution to the phenomenon of super- shedding are underway.

1. Pennsylvania State Univ., University Park, PA
2. Food Safety and Enteric Pathogens Res. Unit USDA, ARS, NADC, Ames, IA
3. Produce Safety and Microbiology USDA, ARS, WRRC, Albany, CA
4. U.S. Meat Animal Res. Ctr., Clay Center, NE