Escherichia coli is a gram-negative, facultatively anaerobic, rod-shaped, coliform bacterium of the genus Escherichia that is commonly found in the lower intestine of warm-blooded organisms. Most E. coli strains are harmless, but some serotypes can cause food poisoning in their hosts. The harmless strains are part of the flora of the gut, and can benefit their hosts by producing vitamin K2. E. coli is expelled into the environment within fecal matter, the bacterium grows massively in fresh fecal matter under aerobic conditions for 3 days, but its numbers decline slowly afterwards. E. coli and other facultative anaerobes constitute about 0. 1% of gut flora, cells are able to survive outside the body for a limited amount of time, which makes them potential indicator organisms to test environmental samples for fecal contamination. A growing body of research, though, has examined environmentally persistent E. coli which can survive for extended periods outside of a host, the bacterium can be grown and cultured easily and inexpensively in a laboratory setting, and has been intensively investigated for over 60 years. E. coli is a chemoheterotroph whose chemically defined medium must include a source of carbon, under favorable conditions, it takes only 20 minutes to reproduce. E. coli is a Gram-negative, facultative anaerobic and nonsporulating bacterium, cells are typically rod-shaped, and are about 2.0 μm long and 0. 25–1.0 μm in diameter, with a cell volume of 0. 6–0.7 μm3. E. coli stains Gram-negative because its cell wall is composed of a peptidoglycan layer. During the staining process, E. coli picks up the color of the counterstain safranin, the outer membrane surrounding the cell wall provides a barrier to certain antibiotics such that E. coli is not damaged by penicillin. Strains that possess flagella are motile, the flagella have a peritrichous arrangement. E. coli can live on a variety of substrates and uses mixed-acid fermentation in anaerobic conditions, producing lactate, succinate, ethanol, acetate. Optimum growth of E. coli occurs at 37 °C, and it uses oxygen when it is present and available. It can, however, continue to grow in the absence of oxygen using fermentation or anaerobic respiration, the ability to continue growing in the absence of oxygen is an advantage to bacteria because their survival is increased in environments where water predominates. The bacterial cell cycle is divided into three stages, the B period occurs between the completion of cell division and the beginning of DNA replication. The C period encompasses the time it takes to replicate the chromosomal DNA, the D period refers to the stage between the conclusion of DNA replication and the end of cell division. The doubling rate of E. coli is higher when more nutrients are available, However, the length of the C and D periods do not change, even when the doubling time becomes less than the sum of the C and D periods. At the fastest growth rates, replication begins before the round of replication has completed, resulting in multiple replication forks along the DNA
Image: E coli at 10000x, original
Scanning electron micrograph of an E. coli colony.
An image of E.coli using early electron microscopy.