Escherichia (named after Theodor Escherich, the person who discovered this genus) is a genus of gram-negative, facultatively anaerobic, rod-shaped bacteria found in the large intestine of humans and other warm-blooded animals. Most species of Escherichia bacteria are either nonpathogenic or opportunistic pathogens.
Many studies have shown that “Escherichia is a genus (or species) made up of phenotypically variable strains”. For many years the genus Escherichia had been represented by a single species, Escherichia coli. However, other species have now been added to the genus. These species include E. adecarboxylata, E. blattae, E. fergusonii, E. hermannii and E. vulneris. E. coli is the type species of the genus Escherichia.
Escherichia bacteria are widely distributed in nature and are part of the indigenous intestinal flora of warm-blooded animals. These bacteria have been isolated from water, soil and clinical samples from humans and animals. E. blattae was isolated from cockroach intestines and do not seem to have been isolated from other sources.