E. coli is a Gram-negative, facultative anaerobe (that makes ATP by aerobic respiration if oxygen is present, but is capable of switching to fermentation or anaerobic respiration if oxygen is absent) 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 colonies on agar.
E. coli on sheep blood agar.
E. coli colonies
E. coli growing on basic cultivation media.
E. coli stains Gram-negative because its cell wall is composed of a thin peptidoglycan layer and an outer membrane. During the staining process, E. coli picks up the color of the counterstain safranin and stains pink. 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.It also attaches and effaces to the microvilli of the intestines via an adhesion molecule known as intimin.
