Escherichia coli (E. coli) is a Gram-negative, facultative anaerobic bacterium commonly found in the lower intestine of warm-blooded animals


While most strains are harmless and form an essential part of the normal gut flora, certain serotypes—most notably O157:H7—are capable of causing severe foodborne illness. Beneficial strains contribute to host health by producing vitamin K2 and helping prevent colonization by pathogenic organisms. Due to its ability to survive temporarily outside the body, E. coli also serves as a key indicator organism for fecal contamination in environmental and water quality testing.



E. coli is one of the most widely studied model organisms in microbiology and biotechnology. Its simple genetics, rapid growth, and adaptability to varied substrates have made it a cornerstone of molecular biology research. Optimal growth occurs at 37°C, though laboratory strains can tolerate higher temperatures. The bacterium can use a range of metabolic pathways, including mixed-acid fermentation under anaerobic conditions and aerobic or anaerobic respiration using diverse redox pairs. Some strains possess peritrichous flagella, enabling motility, while others lack flagella entirely.

Within the species, numerous strains and virotypes differ in their molecular features, physiology, and pathogenic potential. Strains may gain new characteristics through mutation and horizontal gene transfer, enabling them to inhabit specific niches, utilize unique carbon sources, or resist antimicrobial agents. Notable pathogenic groups include enterotoxigenic (ETEC), enteropathogenic (EPEC), enteroinvasive (EIEC), enterohemorrhagic (EHEC), and enteroaggregative (EAggEC) E. coli. These virotypes vary in mechanisms of infection, invasiveness, and toxin production, collectively causing a spectrum of diseases ranging from mild diarrhea to severe complications such as hemolytic uremic syndrome.

While harmless strains colonize the infant gut within the first days of life and remain benign unless acquiring virulence factors, pathogenic strains can cause gastroenteritis, urinary tract infections, neonatal meningitis, peritonitis, septicemia, and pneumonia. Gastrointestinal infection typically results from ingestion of contaminated food or water, with major sources including raw ground beef, unwashed vegetables, unpasteurized dairy, and produce grown in manure-contaminated fields. If E. coli enters sterile body sites, such as the abdominal cavity following perforation of the intestine, it may cause life-threatening infections requiring prompt antibiotic treatment, though the bacterium can rapidly acquire drug resistance.

Epidemiologically, E. coli is transmitted predominantly via the fecal-oral route, with cattle serving as the primary reservoir for O157:H7. Contamination can occur through improper food handling, cross-contamination, unsanitary agricultural practices, or contact with infected animals. Outbreaks have been linked to foods such as spinach, lettuce, seed sprouts, raw milk, and unpasteurized juices. Transmission may also occur through flies, animal contact in petting zoos, and airborne particles in agricultural environments. Preventive measures include proper cooking, pasteurization, hand hygiene, and strict food safety practices to interrupt the cycle of transmission.

Website: cognitivescientist.org 



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