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Escherichia coli

Ah, E. coli, the bug everyone has heard of! A member of the family Enterobacteriaceae, E. coli is a Gram-negative, non-spore-forming rod, ~1-2 µm wide, 3-30 µm long:

The average human gut contains about 1 kg of bacteria. Of these, approximately 0.1% are normally E. coli. The presence of these bacteria within our intestines is necessary for normal development and health - E. coli, along with other types of enterobacteria, synthesize vitamins which are then absorbed by the body, e.g. vitamin K and B-complex vitamins. Although the normal habitat of this species is the gut, they can survive quite well outside the body in faecally-contaminated environments such as water or mud. Under these circumstances, they can be a useful indicator of sewage contamination ("faecal coliforms"). Phase contrast microscopy: E.coli is usually a motile organism, possessing peritrichous flagellae. However, the agar-grown cells in this video are not motile, simply moving due to Brownian motion:

When E. coli go bad ...

Different strains of E. coli are defined serologically by distinctive antigens:

Although most strains of E. coli are harmless and even beneficial, some isolates are capable of causing disease. Pathogenic "enterovirulent" E. coli strains are divided into groups based on pathogenic mechanisms:

 


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