coli

Escherichia coli (E. coli) is a Gram-negative bacterium in the family Enterobacteriaceae. It is a rod-shaped, facultatively anaerobic microorganism commonly found in the lower intestine of humans and warm-blooded animals. The genus and species were named after Theodor Escherich, who first described the organism in 1885. E. coli strains show considerable genetic and phenotypic diversity, ranging from harmless commensals to pathogenic variants.

In the gut, E. coli participates in the normal microbiota and contributes to vitamin production and bowel health. It is also used as an indicator organism for fecal contamination in water quality testing. The species has a well-characterized genome of roughly 4.6 to 5.5 million base pairs, with rapid growth under suitable conditions. Most laboratory strains, such as K-12, MG1655, are nonpathogenic and have been extensively studied as model organisms in molecular biology and genetics.

Pathogenic strains cause disease by producing toxins or by adhering to and damaging intestinal or urinary tract tissues. Major categories include enterotoxigenic (ETEC), enteropathogenic (EPEC), and enterohemorrhagic (EHEC) strains. EHEC, notably the O157:H7 serotype, can cause severe diarrhea and hemorrhagic colitis; some lineages produce Shiga toxins. Transmission commonly occurs through contaminated food or water, or person-to-person spread.

Given its versatility and prominence in both health and disease, E. coli remains a central organism in basic research, biotechnology, and public health. Safety considerations emphasize that pathogenic strains require appropriate containment and handling, while nonpathogenic strains are widely used in education and industry.

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