Clinical Manifestations
Depending on the virulence factors they possess, virulent Escherichia coli strains cause either noninflammatory diarrhea (watery diarrhea) or inflammatory diarrhea (dysentery with stools usually containing blood, mucus, and leukocytes).
Structure, Classification, and Antigenic Types
These are Gram-negative bacilli of the family Enterobacteriaceae. Virulent strains differ from nonvirulent E coli only in possessing genetic elements for virulence factors. Strains producing enterotoxins are enterotoxigenic E coli (ETEC).
Pathogenesis
Transmission is by the fecal-oral route. Pili (fimbriae) allow the bacteria to colonize the ileal mucosa. Cytotonic enterotoxins (encoded on plasmid or bacteriophage DNA) induce watery diarrhea. Plasmid-encoded invasion factors permit invasion of the mucosa, and plasmid- or bacteriophage-encoded cytotoxic enterotoxins induce tissue damage; the presence of either of these factors induces a host inflammatory reaction with an influx of lymphocytes and resulting dysentery.
Host Defenses
Gastric acid and intestinal transit time are important defenses. Specific intestinal immunoglobulin A (IgA) develops and appears to be protective.
Epidemiology
Infection is common where sanitation is poor; both infants and susceptible travelers to developing countries are particularly at risk. The disease is most serious in infants.Copyright © 1996
The University of Texas Medical Branch at Galveston