Escherichia coli, often abbreviated E. coli, are rod-shaped bacteria that tend to occur individually and in large clumps. E. coli are classified as facultative anaerobes, which means that they grow best when oxygen is present but are able to switch to non-oxygen-dependent chemical processes in the absence of oxygen. E. coli bacteria are gram-negative, so they stain pink in a gram test.
E. coli bacteria were first identified by bacteriologist Dr. Escherich in 1885. Since then, more than 700 different serotypes have been identified. Some of these strains are pathogenic, but most are not. A strain known as uropathogenic E. coli, or UPEC, is known to cause urinary tract infections. Another strain, known as O104:H4, has been responsible for many foodborne illness outbreaks in the United States and Europe. Some strains of E. coli, including O157:H7 and O26, produce harmful toxins, which cause severe intestinal illness. These strains are commonly found in uncooked meat and unwashed vegetables that have been exposed to fecal matter.
Harmless strains of E. coli bacteria are present in small numbers in the intestines of healthy humans and animals. These bacteria actually benefit their hosts by producing vitamin K. They can only survive outside the body for a short period of time.