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Unnerstad, H. 2001. Listeria monocytogenes -strain diversity demonstrated by genotyping. Doctoral thesis.

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HISTORYEscherichia coli (Migula) Castellani and Chalmers ( E. coli ) are lactose -fermenting, gram -negative, facultative anaerobic rods, fi rst isolated and characterized by Austrian pediatrician and bacteriologist Theodor Escherich in 1885. 1 Since that time, over 170 serogroups of E. coli have been identifi ed that are distinguished by the expression of O (somatic), H (fl agellar), and/or K (capsular) antigens. Over the last part of the 20th century, several groups of pathogenic E. coli have been identifi ed. Of these serotypes, 43 enterohemorrhagic serotypes of E. coli (EHEC) are associated with bloody diarrhea. 2 E. coli O157:H7 has emerged as the most notorious enterohemorrhagic E. coli serotype based on the threat of these infections to public health. The fi rst recognized outbreak of E. coli O157:H7 occurred in 1982, when an outbreak of food poisoning ( " hamburger diarrhea " ) resulted from the contamination of hamburger with this E. coli serotype. 3 In the United States, E. coli O157:H7 remains among the most common organism isolated from patients with bloody stool specimens. 4 Enteropathogenic E. coli were the fi rst diseasecausing strains of E. coli identifi ed, and these strains of E. coli remain a common cause of diarrhea in children ( " infant diarrhea " ), particularly in developing nations. During the 1960s, enterotoxigenic strains of E. coli were recognized as a cause of " traveler ' s diarrhea. " Enterotoxigenic strains of E. coli remain a major cause of travel -associated diarrhea (Asia, Mexico, Latin America, Africa), as well as gastrointestinal illness in military settings. Recently, enteroaggregative strains of E. coli have been associated with persistent watery diarrhea in developing countries. Each year, 73,000 cases of pathogenic E. coli illness are reported worldwide, resulting in over 60 deaths. 5

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