Transcriptomic Analysis of Rectal-anal Junction Tissue from Super-shedders vs Cattle Negative for E. coli O157:H7

Abstract Text: E. coli O157:H7 is a foodborne pathogen that causes hemorrhagic colitis and hemolytic uremic syndrome in humans. Cattle are the main reservoir for E. coli O157:H7 and individuals shedding > 10⁴ CFU/g of feces are defined as super-shedders. To date, the molecular mechanisms responsible for the high level of carriage and shedding in super-shedders is unknown, but presumably is mediated by a host-microbial interaction. We hypothesized that changes in gene expression related to immune responses in tissues from the rectal-anal junction (RAJ) may be associated with the super-shedder phenomenon. In this study, we performed transcriptomic analysis of tissues from the RAJ, the reported main colonization site of E. coli O157:H7. Total RNA was extracted from RAJ tissues collected from five super-shedder steers and four non-shedder pen mates. RNA sequencing was done using Illumina sequencer Hiseq 2000 with average of 29.7M ± 4.2 M paired-end reads generated from each sample. After mapping the reads to the bovine genome using Tophat, a total of 15,614 expressed genes (FPKM > 0.3) were detected at least once in at least one of the steers, with expression of 13,047 of genes (FPKM > 0.3) detected in non-shedders and 11, 846 (FPKM > 0.3) in super-shedders. The top functions of these genes enriched by GO terms include metabolic process, cellular process, and biological regulation which were not different between the two groups. In total, 20 genes were down regulated in super-shedders as compared to non-shedders (FDR < 0.1, using EdgeR). Of those genes down regulated in super-shedders, 11: CXCL13, CCL21, CCR7, IL2RA, LTB, S100A12, CD19, BANK1, CD19, MS4A1, KLHL6 were predicted to be associated with traits related to immune function; including movement of T-cells, recruitment of leukocytes as well as the levels of B-cells and IgG. This is the first study to report transcriptomic analysis of the RAJ as it relates to the shedding status of the host. Our results suggest that immune homeostasis in super-shedders may play a role in the high levels of shedding observed in these individuals.

Keywords: E. coli O157, super-shedder, transcriptomic analysis