Escherichia coli (E. coli)
|Cell Wall: Gram Negative||Shape: Rod|
|Biochemistry: Lactose Fermenter, Indole Positive|
- Nonpathogenic strains of E. coli are part of the normal GI flora. Pathogenic strains may be acquired from contaminated food and water or transmitted from person-to-person.
- The vast majority of E. coli strains lack virulence factors and comprise the bulk of the normal GI flora. Acquisition of virulence factors are often the cause of pathology and are discussed together with the specific clinical syndrome.
- Pathological E. coli strains are those which have acquired specific virulence factors. Below we list the strains of most clinical import, their associated virulence factors, along with their symptomology. When a strain is not listed these diseases are due to normally non-pathogenic strains of E. coli which infect those with limited or reduced immunity.
- Enteropathogenic E. coli (EPEC)
- Causes a watery, non-bloody infectious diarrhea especially in infants. Possesses factors which allow adherence and effacement of GI mucosa.
- Enterotoxigenic E. coli (ETEC)
- Causes a watery, non-bloody infectious diarrhea and is commonly called "Traveler's Diarrhea". In addition to GI mucosal adherence factors, the strain possess a Heat Labile exotoxin (LT), of the A-B toxin family, that acts similarly to cholera toxin, entering cells, activating adenylyl cyclase, and promoting fluid secretion by enterocytes. Some strains also possess a Heat-stable exotoxin (ST) which worsens diarrhea by further enhancing fluid secretion by enterocytes.
- Shiga-toxin E. Coli (STEC)
- Causes a severe, bloody infectious diarrhea known as "Hemorrhagic Colitis". In addition to GI mucosal adherence factors, the strain secretes an exotoxin highly similar to Shiga Toxin produced by Shigella. Some strains (especially O157:H7) can result in a Microangiopathic Hemolytic Anemia, classically Hemolytic Uremic Syndrome (HUS).
- Enteroinvasive E. coli (EIEC):
- EIEC is the only strain of E. coli which can actually invade the enterocytes of the GI mucosa and thus induces a systemic immune response. Thus in addition to a bloody infectious diarrhea, a fever is induced and white cells (pus) can be observed in the stool. The ability to invade is the result of multiple virulence factors.
- Uropathogenic E. coli
- Possess a specialized pili, termed P. Fimbriae, which allows adhesion to the urothelium. E. coli is the most common cause of UTI especially in young adults and presents with traditional signs of dysuria, frequency, and urgency. If left untreated, complications include cystitis and acute pyelonephritis.
- E. coli is one of the most common causes of meningitis in neonates.
- Bacteremia and sepsis can arise secondary to localized infection and usually occurs in ill patients. E. coli is one of the most common causes of sepsis in hospitalized patients. Septic Shock can ensue if hematological infection is not brought under control
- E. coli is a rather infrequent cause of community-acquired pneumonia but is a common causes of hospital-acquired pneumonia.
- E. coli are developing increasing resistance to common antibiotics. Fluoroquinolones and amoxicillin can be used but bactrim is especially useful for UTIs.