β Scribed by Percival, Steven L.
No coin nor oath required. For personal study only.
Escherichia coli are typically Gram-negative, rod shaped (2.0-6.0 mm in length and 1.1-1.5 mm wide bacilli) bacteria with rounded ends. The actual shape of these bacteria does, however, vary from spherical (cocci) cells through to elongated or filamentous rods. Escherichia coli are non-spore forming, and are usually motile through the action of peritrichous flagella. Escherichia coli are facultatively anaerobic and produce gas from fermentation of carbohydrates, as seen by acid and gas production from lactose at 37 C and 44 C. Most E. coli yield a positive ortho-nitrophenyl-b-D-galactoside (ONPG) reaction, indicating b-galactosidase activity. The methyl red reaction is also positive for E. coli indicating mixed acid fermentation of glucose, but the Voges-Proskauer reaction (acetoin production) is negative. Escherichia coli produce indole, but are unable to hydrolyze urea or grow in MΓΈller's KCN broth (demonstrating an inability to grow in the presence of cyanide). Furthermore, production of hydrogen sulphide is not normally evident when E. coli are cultured on triple sugar iron (TSI) agar or Kligler's iron agar (KIA). Escherichia coli also do not induce gelatin liquefaction through gelatinase activity. The majority of strains decarboxylate lysine, use sodium acetate, but do not grow on Simmons' citrate agar, where citrate is the sole carbon source.Many E. coli cells are capsulated or microcapsulated and these capsules are composed of acidic polysaccharides. Mucoid strains of E. coli produce extracellular slime consisting either of a polysaccharide of certain K antigen specificities, or a common acid polysaccharide (often described as M antigen) composed of colanic acid . Escherichia coli exhibit fimbriae (or pili) of varying structure and antigenic specificity and as these fimbriae are hydrophobic, they provide host-or organ-specific adhesion properties.Several E. coli serogroups are known and the majority are non-pathogenic; however, some groups can cause severe diarrhoeal disease, occasionally with fatal outcome. Escherichia coli is of faecal origin and almost exclusively found in the digestive tract of warm-blooded animals, particularly humans. As a consequence, detection of E. coli in potable water is used as an indicator of human or animal excreta contamination, and is referred to as the coliform index .
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