Escherichia coli (also called E. coli) belong to the genus of Escherichia. It is a gram-negative, rod shape, coliform bacterium of the genus Escherichia. Escherichia coli usually lives in intestines of human and other animals, it can cause cholecystitis, bacteremia, cholangitis, urinary tract infection (UTI), and traveler's diarrhea, and other clinical infections such as neonatal meningitis and pneumonia. Enteric E. coli can be categories based on its virulence nature, such as enteroinvasive E. coli (EIEC), enteropathogenic E. coli (EPEC), enterotoxigenic E. coli (ETEC), enterohemorrageic E. coli (EHEC), verotoxigenic E. coli (VTEC), and enteroadherent aggregative E. coli (EAggEC). Most of stains of E. coli in intestine are not harmful, but pathogenic isolates of E. coli are responsible for infections.
Escherichia coli reproduces by two means: cell division (shown as in Fig.1) and the transfer of genetic material through a sex pilus (conjugation). The most prevalent reproduction for E. coli is asexual reproduction. This begins with the replication of one DNA molecule, then the copies of the genetic material attach themselves to the cell membrane. When the bacterium’s size has doubled from its original size, the cell membrane starts pinching inward, a cell wall is produced between the two DNA molecules. At last, the cell wall divides the cell into two daughter cells.
Fig.1 Cell division of E. coli.
The second process of reproduction of E. coli known as conjugation by which genetic material is transferred between two bacterial cells via a specialized type of fimbriae called sex pili (also known as conjugate fimbriae). Conjugation is more infrequent than cell division, but it allows for a means of genetic diversity between bacteria, and the possibility of beneficial adaptations such as antibiotic resistance. E. coli that contain a fertility factor (F+) know as plasmid undergoes conjugation by first copying its genome. This bacterium is called “the donor”. The donor then releasing an enzyme that contains "mating signal", which showing that it is ready for genetic transfer. This mating enzyme attracts a bacterium that doesn't contain the fertility factor (F-). This bacterium is the recipient. The donor Escherichia coli bacterium connects the sex pilus to the recipient bacterium, and injects the plasmid. Once the pilus is disconnected, the transfer stops.
Fig.2 An example of Bacterial conjugation and recombination.