**1. Introduction**

Bacteriophages (phage) are bacterial viruses that are also known as 'natural killer phages' may take over their bacterial host and use it to grow and multiply. The phage may recognise, infect, and kill specific bacteria or groups of bacteria, as well as their host cells of unrelated bacteria. As a result, they play an important role in bacterial population regulation. Bacteriophages are used to (a) identify specific pathogens to help in pathogen detection and (b) destroy bacterial infections in a process known as lysogeny, in which one bacterium kills another through phage particles [1–4]. Since he first discovered bacteriophages in 1917, and later in 1919, a phage treatment was offered to cure a child suffering from dysentery, and the child was cured of the illness after a single dose of phage administration, D'Herelle is widely regarded as the father of bacteriophages. Since then, the phage cocktail's protection has been verified by administering it to a number of other healthy people [3, 4]. He also noted in 1919 that bacteriophages provided between chickens effectively reduce the mortality of chickens suffering from *Salmonella* infections, indicating that phage therapy experiments against bacterial infections were extremely successful [3–5]. D'Herelle published a comprehensive account of bacteriophages and founded "An International Bacteriophage Institute" in Tbilisi, Georgia, in 1923, which is now known as "the George Eliava Institute of Bacteriophages, Microbiology, and Virology" [3–5]. The Institute is engaged in the production and distribution of therapeutic bacteriophages for the treatment of a variety of bacterial infections. Bacteriophages have been successfully used to treat skin and diarrhoeal infections caused by *Staphylococcus aureus* and *Shigella dysenteriae* [6–8]. However, phage treatment has been poor since the discovery of antibiotics, large-scale development and availability, and widespread clinical use [9–13]. Furthermore, there was a chance of endotoxin contamination since most phage therapy trials lacked random and placebo controls [5]. Overuse and misuse of antibacterial drugs have been recorded since the dawn of the antibiotic era, resulting in intolerable antibiotic resistance with an approximate global intake of 100,000–200,000 tonnes of antibiotics per year [14, 15]. Antibiotic resistance in bacteria has arisen from such indiscriminate prophylactic use of multiple antibiotics, affecting all aspects of life and public health [2, 14–18]. Antimicrobial resistance is becoming a global threat, with the World Health Organization predicting that it could kill at least 50 million people every year by 2050 [19]. As antibiotic resistance rises, researchers are looking for new ways to detect and manage drug-resistant bacterial infections [1, 2, 4, 5]. Antimicrobial-resistant bacteria have evolved from bacteria with intrinsically drug-sensitive genes to bacteria with drug-resistant genes: Multidrug-resistant bacteria are classified as bacteria that are resistant to at least one antimicrobial agent out of three or more, while drug-resistant bacteria are defined as bacteria that are resistant to all antimicrobial stages. The advent and distribution of antimicrobials has increased rapidly due to widespread use of antibiotics as a supplement in animal husbandry, misuse of various antibiotics in clinics [2, 9–11, 13]. Antimicrobials' proliferation and dissemination have accelerated in tandem with international mobility. Existing antibacterial agents were unable to destroy bacteria immune to antibiotics, ushering in the "post-antibiotic" period [9, 14–18, 20–22]. Because of their specific antimicrobial activity as an alternative to antibiotics, bacteriophage treatment is gaining popularity as a means of ensuring future development. When

antibiotics are ineffective against bacterial infections, phage therapy may help eradicate such complicated problems as a reliable treatment choice. In recent years, bacteriophages have been used to biocontrol bacterial numbers in agriculture, veterinary science, aquaculture, and the food industry [2, 10–13]. Bacteriophages have been used in agriculture to combat plant bacterial infections such as *Xanthomonas citri,* which would otherwise be treated with antibiotics. Holins, endolysin, ectolysin, and bacteriocins are bacteriophage antibacterial enzymes. Since endolysin targets induce immediate bacterial lysis, "endolysin therapy" has been developed to exploit their therapeutic potential [23]. Endolysin/recombinant endolysin has a lot of biochemical multiplication, and certain endolysins have a lot of bactericidal activity. Commercial applications have benefited from the use of endolysin enzymes or holins. The development of new drugs, creative methods, and the reduction of the risk of infectious agents and potential factors are all essential components of future bacterial disease control. Phage therapy reduces the development and replication of a wide variety of pathogenic bacteria, enhancing human and animal health and longevity. For particular groups of bacteria, however, the production of specific phage therapy cocktails is desirable. Phage therapy is a great way to treat microbial infections that are different depending on the operating system. Phage therapy is a fascinating rediscovered area of study that has many applications in science, agriculture, veterinary medicine, and medicine, including the potential prevention of antibiotic-resistant pathogens. The ability to combine antibiotic and phage therapy, the use of phage cocktails, and previously unexplored phage protein products are the most promising areas for the effective treatment of drug-resistant bacterial infections. Phage therapy is the subject of global research due to its wide range of applications and uses. This chapter addresses various aspects of phage therapy and how it can be used. After closely studying the protection and efficacy of phage, promising findings indicate that phage therapy against pathogenic bacteria could be the potential solution to pathogens that affect humans and animals.
