EHEC is usually ingested through contaminated food products. Once inside the host, EHEC traverses to colon and establishes itself in the distal ileum or large bowel. Inside the colon, EHEC is thought to use guided motility, provided by flagellar motion, to reach its preferred site of attachment [4]. Autoinducer molecules (AI-2/AI-3) and hormones (epinephrine/norepinephrine) induce various virulence factors and are speculated to help in attachment and subsequent infection process [5]. A two-component system QseBC [6] induces flagellar operon in response to hormones and AI-2/AI-3, resulting in increased and guided motility [4] towards

epithelial cell layer. Upon encountering the epithelial cell layer, the flagella and other surface structures such as

type 1 pili and hemorrhagic coli pilus help EHEC to attach to the surface [7–9]. learn more Multiple environmental and genetic factors such as pH, hormones, signaling molecules as well as quorum sensing (QS) regulate the expression of Locus of enterocyte effacement (LEE) and flagellar operons [10–13]. PD-0332991 cost The hormones and AI-3 also induce type III secretion system (TTSS) in EHEC through QseEF and QseAD [14, 15]. TTSS is encoded in LEE, which is organized in five operons LEE1-LEE5. LEE1-encoded regulator (Ler) is the first gene on LEE1 operon and subject to modulation by various regulators. In turn, Ler activates the transcription of the five operons [13, 15, 16]. The TTSS penetrates the host cell membrane and serves as conduit for injecting effector proteins. These effector proteins manipulate the host machinery including actin Mirabegron cytoskeleton, resulting in attaching and effacing lesions. Some

of the secreted effectors disrupt the tight junction leading to higher secretion of chloride ions and ultimately developing in diarrhea [17]. The phage encoded Shiga toxin is the main virulence factor of EHEC and other Shiga toxin producing E. coli. The Shiga toxin disrupts the protein synthesis in host epithelial cells causing necrosis and cell death [17]. Additionally, Shiga toxin travels to kidney through blood stream and damages renal endothelial cells inciting renal inflammation, potentially leading to HUS [2, 18]. Along with the direct injury to epithelial cells, biofilms formed by pathogenic E. coli strains can pose serious health problems such as prostatitis, biliary tract infections, and urinary catheter cystitis [19]. Antibiotics and antidiarrheal drug therapy of EHEC activates the stress response resulting in induction of phage lytic cycle and subsequent release of Shiga toxin. The release of Shiga toxin is directly correlated with increase in HUS incidence [2, 18]. At present, CDC recommends preventive measures such as washing hands and thorough cooking of meats etc. to control EHEC infections.