S. Typhi has more adhesive proteins on its surface than E. coli. In particular, the higher adhesion in S. Typhimurium results is mainly due to the presence of type 1 fimbriae (T1F) proteins on the cell membrane. These proteins appear as long and thin structures composed of FimA proteins. FimA proteins have a high binding ability to high-mannose oligosaccharides, which are expressed on the human epithelial cell surfaces via FimH adhesion at the top of TIF. Noteworthy, T1F proteins are the most common adhesion proteins in gram-negative bacterial cells where the FimA and FimH are encoded by the fim operon. In addition, the Salmonella genus has at least ten other operons in its genome that encode fimbrins. These additional fimbrins, when expressed, also act like adhesins.
All these structures are absent in E. coli, which explains the low adhesion in the experiment. On its part, E. coli only uses adhesive structures known as bundle-forming pili (BFP) in its adhesion to the host cells. BFP adhesive structures form microcolonies that enhance bacterial resistance to the host defense mechanisms. In addition, these structures are involved in the localized adherence pattern observed in the experiment. Nevertheless, these structures are less adhesive compared to the FimA proteins in S. Typhimurium.