**1. Introduction**

Urinary tract infections (UTIs) are one of the most frequent bacterial infections and the primary causative agent is *Escherichia coli* [1]. The other causative agents reported for UTIs include *Staphylococcus saprophyticus*, *Pseudomonas aeruginosa,* Klebsiella, Enterobacter, and Proteus species [2]. *E. coli*, the primary causative agent of UTI, is a Gram-negative bacteria from the Enterobacteriaceae family. The enteropathogenic strains of *E. coli* are divided into two types: intestinal *E. coli,* which have enteropathogenic E. coli (EPEC), enterohemorrhagic *E. coli* (EHEC), enteroinvasive *E. coli*, enteroaggregative *E. coli*, enterotoxigenic *E. coli* (ETEC). The second category is the uropathogenic *E. coli,* causing extraintestinal infections (**Table 1**). The uropathogenic serotypes 01 0K1, 06:K2, 04:K12, 016:K1, or 018:K5 are associated with the majority of UTIs [3]. Uropathogenic *E. coli* causes both complicated and uncomplicated UTIs. UPEC has fimbria as an important virulence factor. These fimbriae contain subunit protein (pap A) encoded by papA gene [4]. The type I fimbriae are most commonly expressed adhesins that allow the bacteria to attach and colonize the human urogenital tract. The type I fimbriae constitutes of Fim H protein (responsible for binding), Iaminin (part of extracellular matrix), and secretory Ig A. Another fimbriae present in UPEC is P fimbriae (PapG) adhesion of p fimbriae mediates the bacterial binding, thus inducing UTI symptoms [4]. Other



virulence factors in UPEC are F1C and S fimbriae enclosing the fac and sfa gene, cytotoxic necrotic zing factor (NF1), iron-binding siderophores, and K1 capsular polysaccharide.

Bacteriophages are viruses that attack bacteria. Antimicrobial resistance by bacteria has now become a global threat and could kill 50 million people by the year 2050 as per the World Health Organization estimates [5]. Phages are now known to cure antibiotic-resistant bacterial infections as well as decrease bacterial virulence by overcoming the barriers bacteria used to avoid them. Bacteriophages are now being explored as potential therapeutic tools for the elimination of bacterial pathogens. Bacteriophages can disrupt pathogenic processes associated with biofilm and exopolysaccharide formation by microflora. Bacteriophage therapy is a promising strategy to control bacterial infections as phages are very efficient in killing host bacteria and do not disrupt other flora and have a low cost of production [6]. Antibiotics used alone have a broad spectrum of activity inducing drug resistance in bacteria and are toxic, whereas phages are non-toxic [7]. Using other strategies, such as herbal products, is more costly and less efficient and has a broad spectrum when compared with phages that are safe and efficient even through oral administration [8]. The combination of antibiotics and phage therapy and the use of phage cocktails have great potential in the treatment of drug-resistant bacterial infections, particularly UTIs. This chapter focuses on the use of phages in treating UTIs caused by uropathogenic *E. coli.*
