Escherichia coli

Escherichia coli

Organism

Escherichia coli is a moderately-sized gram-negative bacillus.
Possess a peritrichous (def) arrangement of flagella.
Facultative anaerobe (def).

Habitat

Normal flora of the intestinal tract in humans and animals.

Source

Usually the patient's own fecal flora; some transmission is patient-to-patient.

Clinical Disease

E. coli causes around 80 percent of all uncomplicated urinary tract infections (UTIs) and more than 50 percent of nosocomial (def) UTIs. UTIs account for more than 7, 000,000 physician office visits per year in the U.S. Between 35 and 40 percent of all nosocomial infections, about 900,000 per year in the U.S., are UTIs and are usually associated with urinary catheterization (def).
E. coli causes wound infections, usually a result of fecal contamination of external wounds or a result of wounds that cause trauma to the intestinal tract, such as surgical wounds, gunshot wounds, knife wounds, etc.
E. coli is by far the most common gram-negative bacterium causing sepsis. Septicemia (def) is a result of bacteria getting into the blood. They are usually introduced into the blood from some other infection site, such as an infected kidney, wound, or lung. There are approximately 500,000 cases of septicemia per year in the U.S. and the mortality rate is between 20 and 50 percent. Over 175,000 people a year in the U.S. die from septic shock. Approximately 45 percent of the cases of septicemia are due to gram-negative bacteria. Klebsiella, Proteus, Enterobacter, Serratia, and E. coli, are all common gram-negative bacteria causing septicemia.
E. coli, along with group B streptococci, are the leading cause of neonatal meningitis (def).
While E. coli is one of the dominant normal flora in the intestinal tract of humans and animals, some strains can cause gastroenteritis, an infection of the intestinal tract.
- Enterotoxigenc E. coli (ETEC) produce enterotoxins that cause the loss of sodium ions and water from the small intestines resulting in a watery diarrhea. Over half of all travelers' diarrhea is due to ETEC; almost 80,000 cases a year in the U.S.
- Enteropathogenic E. coli (EPEC) cause an endemic diarrhea in areas of the developing world, especially in infants younger than 6 months. The bacterium disrupts the normal microvilli (def) on the epithelial cells of the small intestines resulting in maladsorbtion and diarrhea.
- Enteroaggregative E. coli (EAEC) is a cause of persistant diarrhea in developing countries. It probably causes diarrhea by adhering to mucosal epithelial cells of the small intestines and interfering with their function.
- Enteroinvasive E. coli (EIEC) invade and kill epithelial cells of the large intestines causing a dysentery-type syndrome similar to Shigella common in underdeveloped countries.
- Enterohemorrhagic E. coli (EHEC), such as E. coli 0157:H7, produce a shiga-like toxin that kills epithelial cells of the large intestines causing hemorrhagic colitis, a bloody diarrhea. In rare cases, the shiga-toxin enters the blood and is carried to the kidneys where, usually in children, it damages vascular cells and causes hemolytic uremic syndrome. E. coli 0157:H7 is thought to cause more than 20,000 infections and up to 250 deaths per year in the U.S.
- Diffuse aggreegative E. coli (DAEC) causes watery diarrhea in infants 1-5 years of age. They stimulate elongation of the microvilli on the epithelial cells lining the small intestines.

Pathogenicity

In the outer membrane of the gram-negative cell wall, the lipopolysaccharide functions as an endotoxin . Endotoxin, especially when in the blood, can lead to inflammation, high fever, hypotension, capillary damage, intravascular coagulation, tissue degradation, and irreversible shock. Death is a result of what is called the shock cascade (see Fig. 1).
Various types of pili (def) enable the bacterium to initially adhere to epithelial cells of the mucous membranes.
A variety of cell wall adhesins (def) enable the bacterium to make a more intimate contact with the mucous membranes.
Some strains (ETEC) secrete enterotoxins that cause the loss of sodium ions and water from the small intestines resulting in a watery diarrhea.
Some strains (EHEC) secrete a shiga-like toxin that kills epithelial cells of the large intestines causing hemorrhagic colitis (def), a bloody diarrhea.

Treatment

Uncomplicated symptomatic acute cystitis and/or urethritis are usually treated for three days with trimethoprim-sulfamethoxazole (TMP-SMX), norfloxacin, or ciprofloxacin* (see antibiotic table). In vitro antibiotic susceptibility tests usually guide treatment of more complicated infections.

*Drugs may change with time.

For a more detailed article on Escherichia coli infections, see Escherichia coli infections, by Chi Hiong U Go, MD, Assistant Professor, Department of Internal Medicine, Texas Tech University Health Science Center at Odessa and Burke A Cunha, MD, Professor of Medicine, State University of New York at Stony Brook School of Medicine; Chief, Infectious Disease Division, Vice-Chair, Department of Internal Medicine, Winthrop-University Hospital