page_title: Escherichia coli
section_title: Type and morphology
hierarchical_section_title: Escherichia coli / Biology and biochemistry / Type and morphology
caption_attribution_description: English: Escherichia coli grows on many commonly used cultivation media. Examples of these media are: Fig. A1 Brain heart infusion agar (BHIA), A2 Trypticase soy agar (TSA), A3 MacConkey agar (MCA), A4 Endo agar Fig. B shows growth of a common E. coli strain on these media. Note the different size of colonies as nutriet and selective properties of these media vary. Colonies on brain heart infusion agar (B1) are larger in comparison with colonies on trypticase soy agar (B2), MacConkey (B3) and Endo agar (B4). MacConkey (Fig. C1, C4) and Endo agar (Fig. C2, C3) represent diagnostic selective media. Both of them typically inhibit growth of Gram positive bacteria and enable differentiation between lactose positive and lactose negative bacteria (E. coli is typically lactose positive).Colonies are smallest on Endo agar as this medium has higher selectivity for Enterobacteriaceae in comparison with MacConkey agar. Size of colonies is also influenced by numbers of colonies growing on a defined surface of agar medium (higher numbers usually mean smaller colonies). (Competition for nutrients) Fig. C E. coli growing on MacConkey (C1) and Endo agar (C2) in comparison with Klebsiella pneumoniae (C3 MacConkey, C4 Endo). Both of them are lactose positive. Fig. D, G, H Colonies of lactose-negative and positive E. coli on MacConkey agar. E. coli strains are typically lactose positive. Colonies apperaing lactose-negative are usually delayed lactose fermentors giving positive ONPG test. Fig. E Staphylococcus aureus (yellow), Enterococcus faecalis (small) and E. coli on trypticase soy agar after 24 h at 37°C. Seen with reflected light. Fig. F E. coli and Pseudomonas aeruginosa (smaller greenish colonies) in mixed culture on brain heart infusion agar. 24 h, 37°C, seen with both reflected and transmitted light. Fig. I E. coli and Klebsiella pneumoniae (larger), yellow, lactose-positive colonies on CLED agar. Bluish lactose-negative colonies of Serratia marcescens. Fig. J Lactose-fermenting colonies of E.coli with a gold metallic sheen on Endo agar.
context_page_description: Escherichia coli, also known as E. coli, is a Gram-negative, facultative 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 serious food poisoning in their hosts, and are occasionally responsible for food contamination incidents that prompt product recalls. The harmless strains are part of the normal microbiota of the gut, and can benefit their hosts by producing vitamin K₂, and preventing colonisation of the intestine with pathogenic bacteria, having a symbiotic relationship. 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 microbiota, and fecal–oral transmission is the major route through which pathogenic strains of the bacterium cause disease. 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.
context_section_description: 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 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.
caption: E. coli growing on basic cultivation media.
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