**2. The discovery of** *Escherichia coli*

The bacterium *E. coli* was discovered by the German-Austrian pediatrician Dr. Theodor Escherich (1857–1911) in 1885 [2]. He conducted examinations of neonate's meconium and feces of breast-fed infants with the aim to gain insight into the development of intestinal "flora." In preparations of meconium and stool samples under the microscope, he observed "slender short rods" of the size of 1–5 μm in length and 0.3–0.4 μm in width, which he named *Bacterium coli commune* (**Figure 2**). Further, he cultured these bacteria on agar and blood serum plates, where these bacteria grew as white, non-liquefying colonies. He also showed that these bacteria slowly cause milk to be clotted, as a result of acid formation, and

#### **Figure 2.**

*Escherich's drawing of the stool bacteria, as seen under light microscope [4]. Panel 1: Preparation of a meconium of a 27-hour-old infant. The E. coli as Bacterium coli commune is represented under d. Panel 2: Preparation of a stool of a 2-month-old healthy breast-fed child. The E. coli as Bacterium coli commune is represented under a and a*′*.*

demonstrated that these bacteria have fermentative ability. He also performed the Gram method of staining and revealed that these bacteria rapidly take color with all aniline dyes but lose the color after treatment with potassium iodide and alcohol [2]. Later, in 1919, the bacterium was renamed after its discoverer by Castellani and Chalmers and became *Escherichia coli* [3].

**5**

*Introductory Chapter: The Versatile Escherichia coli DOI: http://dx.doi.org/10.5772/intechopen.88882*

**3. Characteristics of** *Escherichia coli*

The bacterium *E. coli* (**Figure 3**) belongs into the family of *Enterobacteriaceae*. It is a Gram-negative rod-shaped bacterium, non-sporulating, nonmotile or motile by peritrichous flagella, chemoorganotrophic, facultative anaerobic, producing acid

*E. coli* is a well-known commensal bacterium that is among the first colonizing bacteria of the gut after birth. It is a highly successful competitor in the human gut and is comprising the most abundant facultative anaerobe of the human intestinal microbiota [7]. As it is a facultative anaerobe, it survives when released to the environment and can be spread to new hosts. *E. coli* is thus an important component of

Even though *E. coli* is a well-known commensal bacterium, many pathogenic strains of *E. coli* do exist. Several highly adapted *E. coli* clones have acquired specific virulence factors, which confer an increased ability to adapt to new niches and allow them to cause a broad spectrum of disease, and intestinal and also extraintestinal infections [7].

The first complete *E. coli* genome sequence was the sequence of the K-12 MG1655 strain of *E. coli*, published in 1997. The sequenced strain has been maintained as a laboratory strain with minimal genetic manipulation, having only been cured of the temperate bacteriophage lambda and F plasmid. The published genome has 4,639,221 base pairs. Protein-coding genes account for 87.8% of the genome, 0.8% encodes stable RNAs, and 0.7% consists of noncoding repeats. Eleven percent of the genome are involved in regulation of gene expression and also other functions [9].

*Scanning electron microscopy of a single bacterial E. coli cell adhering to 19-day-old Caco-2 cells [6].*

The map is based on the K-12 MG1655 sequence data as deposited in GenBank (Accession number NC\_000913) [10]. The multiplier for the ticks is 1e-6 (1.0 represents 1,000,000). In blue, the forward genes are shown, in purple the reverse genes, tRNA genes in orange, and rRNA genes in red. The map was drawn with

A circular map of the *E. coli* genome is represented in **Figure 4**.

from glucose, catalase positive, oxidase negative, and mesophilic [5].

**3.1 Basic characteristics**

the biosphere [8].

**3.2 The** *E. coli* **genome**

**Figure 3.**
