UnderstandingEscherichia coliO157:H7 and the Need for Rapid Detection in Water

Abstract

Escherichia coli is a facultative anaerobe that commonly inhabits the gastrointestinal tracts of humans within hours of birth. This gram‐negative bacillus of the family Enterobactericeae is normally a harmless commensal that helps the host by suppressing pathogenic bacteria (due to competition) and by producing vitamin K and vitamin B complex (1). Individuals who suffer severe immunosuppression (both acquired and due to chemotherapy) or a breached gastrointestinal barrier can experience infection by nonpathogenic E. coli . More likely, however, are instances of infection by pathogenic E. coli that can include urinary tract infections, sepsis/meningitis, or diarrhea. Within the pathogenic E. coli responsible for diarrheagenic disease, differentiation of the strains has led to development of five classes (virotypes): enteropathogenic E. coli (EPEC), enterohemorrhagic E. coli (EHEC), enterotoxigenic E. coli (ETEC), enteroinvasive E. coli (EIEC), and enteroaggregative E. coli (EAEC) (2). Differentiation of pathogenic strains of E. coli is based on the organism's surface antigen profiles of O (somatic), H (flagellar), and K (capsular). This serological classification was originally proposed by Kauffman in 1944 and a modified form is still in use today. Although this serotyping of E. coli is a reproducible mechanism for identifying E. coli associated with particular clinical disease, the serotypes themselves are not responsible for virulence but are only identifiable chromosomal markers for virulence factors (2). This article focuses on E. coli O157:H7, a member of the EHEC class of diarrheagenic E. coli , and specifically discusses transmission routes, particularly focused on the waterborne route and the methods that may be employed for detecting contamination.