The Carbon Starvation-Inducible Lipoprotein (Slp) Influences Differential Adherence of Escherichia coli O157:H7 at the Bovine Rectoanal Junction.
Shiga toxin-producing Escherichia coli O157:H7 (O157), a foodborne human pathogen, persists at the rectoanal junction (RAJ) of the bovine intestinal tract, in asymptomatic cattle reservoirs. Identifying mechanisms used by O157 for initial adherence before persistence at the RAJ could help develop effective O157 control modalities. We recently established the role of carbon starvation-inducible lipoprotein (Slp) in initial adherence of O157 to Caco-2 cells, with the human polymeric immunoglobulin receptor (pIgR) protein as the Slp-receptor. Here, we evaluated the role of Slp in O157 adherence to the bovine RAJ using the RAJ squamous epithelial (RSE) cell- and RAJ-In vitro Organ Culture (IVOC)- adherence assays. The wild-type O157 strain EDL932 (EDL932-WT), its isogenic slp deletion mutant (EDL932 {Delta}slp), and the slp complemented mutant (EDL932 {Delta}slp-p:slp), were tested with no bacteria controls. Adherence was verified by culture and immunofluorescence (IF) staining of O157. Tissue integrity was determined using nuclear/cell staining dyes and histopathological examination. All test strains adhered in a diffuse-moderate pattern on RSE cells. However, differential adherence was observed on the RAJ-IVOC with the strains preferentially adhering to the columnar cells. Additionally, EDL932- WT and EDL932 {Delta}slp-p:slp strains adhered in slightly greater numbers than the EDL932 {Delta}slp strain to the RAJ-IVOC, causing disruptions primarily in the columnar region of otherwise intact RAJ-IVOC tissues. Interestingly, pIgR was also predominantly detected by IF microscopy and RNAscope in situ hybridization at the columnar region of the RAJ-IVOC tissue. In silico modeling demonstrated the possibility of a bovine pIgR- bacterial Slp interaction. Hence, our observations support the role for Slp in the initial adherence of O157 to the columnar cells at the bovine RAJ, unlike the squamous cells where the loss of slp did not impact attachment. In addition, a possible mucosal immune-interference resulting from the bovine pIgR-Slp interaction could contribute towards long-term O157 colonization of cattle. AUTHOR SUMMARYEscherichia coli O157:H7 (O157) is a foodborne pathogen that causes disease in humans with symptoms ranging from watery/bloody diarrhea to kidney failure. Cattle are the main reservoirs of this human pathogen, where O157 tends to persist at the rectoanal junction (RAJ) of the bovine gastrointestinal tract. However, the exact mechanisms by which O157 adheres and persists at the bovine RAJ is not fully understood. Here, we identified that the O157 carbon starvation-inducible lipoprotein (Slp) allows O157 to attach to cells at the RAJ using polymeric immunoglobulin receptor (pIgR) protein as the Slp-receptor. Not only does this attachment of Slp to the cattle receptor allow O157 to colonize cattle, but the interaction could potentially interfere with intestinal immune responses, further promoting long-term O157 colonization of cattle. This makes Slp an attractive target for therapeutic interventions, such as vaccines that could interfere with O157 attachment to cattle intestinal cells.