**4.4 Extracellular polysaccharides**

There are a variety of extracellular polysaccharides produced by *E. coli* such as O antigen, core polysaccharides of LPS (lipopolysaccharide), colonic acid or capsule, etc. Their role in the pathogenesis of UTI is not well understood. `LPS of UPEC is

regarded important in stimulating proinflammatory response in cases of uncomplicated UTI. Also, it is also noted in animal models that acute renal failure due to LPS is not dependant on the presence of functional LPS receptors TLR4 in the kidney but systemic response to LPS.

The capsule is known to provide protection against phagocytosis and complementmediated bactericidal effect in the host. In addition, it has been found that the K2 capsule and not the K54 capsule acts to be confirmed urovirulence factor [3, 37].

#### **4.5 Proteases**

Proteases are enzymes that leads to the cleavage of peptide bonds. They are generally found in mobile genetic elements like transposons, plasmids or prophages [38]. Although, they are not needed for the survival and replication of bacteria, they may be vital for virulence.

Omptins are considered outer-membrane proteases seen in various members of the Enterobacteriaceae family. *E. coli* can encode upto 3 omptims such as *ompT, ompP and arlC* [39]. OmpT have been recognized as a significant virulence factor in UPEC strains causing cystitis, pyelonephritis, urosepsis as opposed to asymptomatic strains [39].

#### **4.6 Flagella**

Flagella is an organelle that accounts for the motility in bacteria and flagellated UPEC is responsible for nearly about 70–90% of all UTIs. Genes for synthesis of flagella form a well-regulated and directed cascade of three 3 classes*.* The benefits of having flagella mediated motility by *E. coli* during colonization of the urinary tract include the capability of dissemination to new sites of the urinary tract to obtain nutrients and in addition to escape from immune responses of the host [4].

#### **4.7 Chemotaxis**

Chemotaxis is generally a behavior that is used by the bacteria to sense and then respond to external chemical signals. There are mainly four chemotaxis protein receptors that are necessary for chemotaxis in *Escherichia coli* such as Tar and Tsr (amino acids), Trg (saccharides) and Tap (dipeptides) [40]. There is an observation of *tar* and *tsr* being present in 100% and 98% of all motile UPEC isolates respectively. While *trg* and *tap* were found significantly less among UPEC in comparison to fecal isolates [41].
