Abundance and Expression of Shiga Toxin Genes in at the Recto-Anal Junction Relates to Host Immune Genes.

Shiga toxin (Stx) is the main virulence factor of Shiga toxin-producing  (STEC), and ruminants are the main reservoir of STEC. This study assessed the abundance and expression of genes and the expression of host immune genes, aiming to determine factors affecting these measures and potential gene markers to differentiate gene expression in the recto-anal junction of feedlot beef cattle. Rectal tissue and content samples were collected from 143 feedlot steers of three breeds (Angus, Charolais, and Kinsella Composite) over 2 consecutive years 2014 (n=71) and 2015 (n=72). The abundance and expression of  and  were quantified using qPCR and reverse-transcription-qPCR (RT-qPCR), respectively. Four immune genes (, and ), previously reported to be down-regulated in super-shedder cattle (i.e., > 10 CFU g) were selected, and their expression was evaluated using RT-qPCR. The gene abundance was only detected in tissue samples collected in year 2 and did not differ among breeds. The gene was detected in STEC from all samples collected in both years and did not vary among breeds. The abundance of and  differed (P < 0.001) in content samples collected across breeds (:AN>CH>KC, : AN=CH>KC) in year 1, but not in year 2. Expression of was detected in 13 RAJ tissue samples (2014: n=6, 2015: n=7), while expression of was not detected. Correlation analysis showed that the expression of was negatively correlated with the expression of  (R=-0.56, P=0.05) and positively correlated with the expression of (R=0.60, P=0.05). The random forest model and Boruta method revealed that expression of selected immune genes could be predictive indicators of expression with prediction accuracy of  > > >. Our results indicate that the abundance of could be affected by cattle breed and sampling year, suggesting that host genetics and environment may influence STEC colonization of the recto-anal junction of feedlot cattle. Additionally, the identified relationship between expressions of host immune genes and suggests that the host animal may regulate expression in colonizing STEC through immune functions.