Fig 5. Proposed model for the controlled expression and secretion of virulence factor ChiA in S. Typhimurium.

Upon contact with polarized IEC, mucin glycoproteins of the mucus layer induce the expression of the inner membrane-bound transcriptional regulator ChiR. ChiR accumulation subsequently leads to the induction of ChiA expression. Once ChiA is expressed, it is efficiently secreted by a holin/peptidoglycan hydrolase-dependent protein secretion system, also referred to as the Type 10 Secretion System (T10SS). Secreted ChiA then promotes the adherence of S. Typhimurium to intestinal epithelial cells, followed by increased invasion into these host cells. The model was created using biorender.com.