**2. What is uropathogenic** *E. coli***? How it causes infection?**

## **2.1 Uropathogenic** *E. coli*

*Escherichia coli*, a Gram-negative bacilli belonging to the family Enterobacteriaceae resides in the gastrointestinal tract of humans as a part of their microbiota. It normally remains in harmony with its host and seldom causes disease except in an immunocompromised host. However, few strains of *E. coli* can split from their commensal cohort taking on a pathogenic form. That means these strains acquire specific virulence factors through plasmids, pathogenicity islands or DNA horizontal transfer of transposons that bestow them the ability to adjust to new niches and cause a broad spectrum of diseases [4]. Further, only the most successful combinations of virulence factors persist to become specific pathotypes of *E. coli* [4]. The strains of *E. coli* which are pathogenic are divided into diarrheagenic or enteric *E. coli* and extraintestinal *E. coli* (EXPEC) based on the body site they colonize. Diarrheagenic *E. coli* includes enterotoxigenic (ETEC), enteropathogenic (EPEC), shiga toxin-producing (STEC), enteroaggregative (EAEC), enteroinvasive (EIEC), and diffusely adherent *E. coli* (DAEC). While EXPEC is mainly uropathogenic *E. coli* (UPEC), neonatal meningitis *E. coli* (NMEC) and sepsis-associated *E. coli.* Based on phylogenetic analysis using multilocus enzyme electrophoresis, pathogenic *E. coli* pathotypes (from both intestinal and extra-intestinal *E. coli*) were divided into four phylogenetic groups A, B1, B2 and D. These phylogenetic groups are representative of their genetic origin [5].

Uropathogenic *E. coli* as described belongs to the extraintestinal pathogenic *E. coli* group and is associated with a subset of serogroups and serotypes (O1:H4, O1:H6, O1:H7, O1:H− , O2:H1, O2:H4, O4:H5, O6:H1, O7:H4, O7:H6, O7:H− , O18ac:H7, O18ac:H− , O22:H1, O25:H1, O75:H5 & O75:H7) and with the B2 or D phylogenetic groups [6]. UPEC possesses acquired virulence and resistant determinants which permits it to victoriously colonize the urinary tract and cause disease.

#### *2.1.1 CFT073*

CFT073 is a prototypical strain of UPEC that was recovered from a woman having severe pyelonephritis infection, it belongs to phylogenetic group B2. It was noted to have increased hemolytic activity in comparison to other UPEC strains. On sequencing, its virulence genes were found to be grouped into five pathogenicity islands [7, 8].
