Escherichia Coli

Escherichia coli is a gram-negative, facultatively anaerobic rod belonging to the Enterobacteriaceae family.  It was first described by Theodor Escherich (hence the name Escherichia) in 1885.  E coli is one of the most common gastrointestinal commensal organisms.  Although most strains are harmless, the acquisition of virulence factors (eg, from a bacteriophage or plasmid) can result in pathogenicity.  E coli is a leading cause of diarrheal illness, as well as infections of the urinary tract and nosocomial and neonatal infections.

E coli is a gram-negative, facultatively anaerobic, rod-shaped bacterium that is readily cultured from stool on selective media (eg, MacConkey agar) under aerobic conditions.  All strains are oxidase negative, the majority (>99%) produce indole, and most (~90%) ferment lactose.

Most strains are harmless and exist as commensal organisms in the gastrointestinal tract.  Pathogenic strains emerge when the bacterium acquires virulence genes via plasmids, transposons, bacteriophages, and/or pathogenicity islands.  Pathogenic subtypes are generally categorized based on antigens for lipopolysaccharide (O antigen) and flagella (H antigen).  Common pathogenic subtypes and their clinical features are described below.