AUTHOR=Pan Zhe , Chen Yanhong , McAllister Tim A. , Gänzle Michael , Plastow Graham , Guan Le Luo 

TITLE=Abundance and Expression of Shiga Toxin Genes in Escherichia coli at the Recto-Anal Junction Relates to Host Immune Genes

JOURNAL=Frontiers in Cellular and Infection Microbiology

VOLUME=11

YEAR=2021

URL=https://www.frontiersin.org/journals/cellular-and-infection-microbiology/articles/10.3389/fcimb.2021.633573

DOI=10.3389/fcimb.2021.633573

ISSN=2235-2988

ABSTRACT=<p>Shiga toxin (Stx) is the main virulence factor of Shiga toxin-producing <italic>Escherichia coli</italic> (STEC), and ruminants are the main reservoir of STEC. This study assessed the abundance and expression of <italic>Stx</italic> genes and the expression of host immune genes, aiming to determine factors affecting these measures and potential gene markers to differentiate <italic>Stx</italic> 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 <italic>stx1</italic> and <italic>stx2</italic> were quantified using qPCR and reverse-transcription-qPCR (RT-qPCR), respectively. Four immune genes (<italic>MS4A1, CCL21, CD19</italic>, and <italic>LTB</italic>), previously reported to be down-regulated in super-shedder cattle (i.e., &gt; 10<sup>4</sup> CFU g<sup>-1</sup>) were selected, and their expression was evaluated using RT-qPCR. The <italic>stx1</italic> gene abundance was only detected in tissue samples collected in year 2 and did not differ among breeds. The <italic>stx2</italic> gene was detected in STEC from all samples collected in both years and did not vary among breeds. The abundance of <italic>stx1</italic> and <italic>stx2</italic> differed (P &lt; 0.001) in content samples collected across breeds (<italic>stx1</italic>:AN&gt;CH&gt;KC, <italic>stx2</italic>: AN=CH&gt;KC) in year 1, but not in year 2. Expression of <italic>stx2</italic> was detected in 13 RAJ tissue samples (2014: n=6, 2015: n=7), while expression of <italic>stx1</italic> was not detected. Correlation analysis showed that the expression of <italic>stx2</italic> was negatively correlated with the expression of <italic>MS4A1</italic> (R=-0.56, P=0.05) and positively correlated with the expression of <italic>LTB</italic> (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 <italic>stx2</italic> expression with prediction accuracy of <italic>MS4A1</italic> &gt;<italic>LTB</italic> &gt;<italic>CCL21</italic> &gt;<italic>CD19</italic>. Our results indicate that the abundance of <italic>Stx</italic> 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 <italic>stx2</italic> suggests that the host animal may regulate <italic>stx2</italic> expression in colonizing STEC through immune functions.</p>