**1. Introduction**

The bacteria *Escherichia coli* was discovered by German pediatrician Theodor Escherich (1857–1911), who isolated it from babies' feces in 1885 [1]. *E. coli* is a gram-negative, non-sporulating, rod-shaped, facultative anaerobic, and coliform bacterium pertaining to the genus *Escherichia* that commonly inhabits the environment, foods, and warm-blooded animals' lower gut [2]. In the domains of biotechnology and microbiology, it is the most widely studied prokaryotic model organism. It can live for long periods of time in feces, soil, and water, and is frequently used as a water contamination indicator organism. For 2–3 days, the bacterium multiplies rapidly in fresh feces under aerobic circumstances, but its numbers gradually fall after that. *E. coli* is gram-negative, straight, rod-shaped, non-sporing, non-acid fast, and bacilli that exist in single and pairs. Cells are typically rod-shaped, with 1–3 μm × 0.4–0.7 μm (micrometer) in size around 1 μm long, 0.35 μm wide, and 0.6–0.7 μm in volume [3]. It is motile due to peritrichous flagellar arrangement, and very few strains are non-motile. The optimal growth of *E. coli* occurs at 37°C (98°F) but some laboratory strains can multiply at temperatures of up to 49°C (120.2°F). It takes as little as 20 min to reproduce in favorable conditions [4]. Fimbriated strains exist both as motile and non-motile. A polysaccharide capsule has been discovered in some *E. coli* strains isolated from extraintestinal infections. The *E. coli* capsules can be clearly seen using negative staining procedures, which produce a bright halo over a dark

backdrop. They have a thin cell wall with only one or two layers of peptidoglycan [5] as shown in **Figure 1**.

It colonizes a newborn's gastrointestinal (GI) tract within hours after birth and even helps to keep our digestive tract healthy. Several strains of *E. coli* have been identified as good and effective probiotics and are currently employed in pharmaceuticals. It truly is a facultative anaerobic chemoorganotroph capable of both respiratory and fermentative metabolism [7]. Although most strains of *E. coli* are safe, some serotypes can induce diarrhea when consumed through contaminated food or drink, while others might cause urinary tract infections (UTIs), anemia, and respiratory or kidney infections [8]. However, certain strains have developed into pathogenic *E. coli* by using plasmids, transposons, bacteriophages, and/or pathogenicity islands to acquire virulence factors [9]. Serogroups, pathogenicity mechanisms, clinical signs, and virulence factors can all be used to classify the pathogenic strain of *E. coli* [10].

The bacterium can be grown easily and inexpensively in a laboratory setting under appropriate conditions. It takes as little as 20 min to reproduce and has been intensively investigated for over 60 years [11]. *E. coli* is the most widely studied prokaryotic model organism and an important species in the field of biotechnology and microbiology, where it serves as the host organism for recombinant DNA and experimental workhorse for DNA manipulation and protein production [12].
