Global properties:
Members of the genus Escherichia are common bacteria that colonize the human large intestine. Most are opportunistic normal flora but some are potent pathogens.
Transmission of diarrheal disease is generally person to person, usually related to hygiene, food processing and sanitation.
Four general categories of pathogenic E. coli are recognized:
- Enterotoxigenic (ETEC)
- Enteroinvasive or "Shigella-like" (EIEC)
- Enteropathogenic (EPEC)
- Enterohemorrhagic (EHEC)
Different groups are most often delineated by serology, in particular, by the immunogenic character of the O (somatic, LPS) and H (flagellar) antigens.
Distinctive properties:
Escherichia are Gram-negative bacilli that ferment lactose. Most are motile by peritrichious flagella.
Escherichia possess a typical Gram-negative cell wall containing LPS.
Approximately 170 different O antigens have been delineated and some of these are cross-reactive with Shigella, Salmonella and Klebsiella.
Motile strains possess H (flagellar) antigens that can be used for epidemiologic purposes.
Escherichia also possess K (capsular) antigens similar to the Vi antigen of Salmonella.
Enterotoxigenic strains may also display colonization factor antigens (CFA/I, CFA/II).