E.coli

Escherichia Coli commonly known as E.coli is found in the normal flora of the colon and intestines. As the normal flora it causes no problems but if combined with a virulence factor it can cause different diseases like:

1.      Diarrhea

2.      Urinary tract infection

3.      Neonatal Meningitis

4.      Gram negative sepsis

5.      Hospital acquired pneumonia

Mucosal interactions:

Pilli: these help invade the intestines

The bacteria produce different types of Exotoxins which are as follows:

1.      Heat Labile Toxin

2.      Heat Stable toxin

3.      Shiga like Toxin

This bacteria also produces endotoxin which is:

·         Lipid A of Lipopolysaccaride (LPS)

Reservoirs: Human and animals

Transmission: Fecal oral route. Example: ingestion of contaminated food and water, during birth, normal flora.

Characteristics of E.coli:

·         Straight gram negative rods.

·         Ferment lactose.

·         Facultative anaerobe.

·         Oxidase negative

E.coli Diarrhea:

Diarrhea caused by E.coli is most common in infants. Death usually occurs due to dehydration. Traveller’s diarrhea is due to contamination.

The types of diarrhea produced by E.coli depends on the virulence factors of E.coli. These are:

1.      Enterotoxigenic E.coli (ETEC):

This is the virulence factor that causes traveler’s diarrhea.

Pilli present on the surface of E.coli binds to the intestinal epithelial cells and the Heat labile and Heat stable exotoxins are released. These in turn inhibit the sodium and chloride reabsorption from the intestinal lumen and stimulate secretion of chloride and bicarbonates, water in turn follows them into the intestinal lumen and thus diarrhea occurs. This is also known as rice watery diarrhea and resembles the diarrhea cause by Vibrio Cholera.

2.      EnteroHemorhagic E.coli (EHEC):

Antibiotics increase the chances of hemolytic uremic syndrome (HUS). In HUS the patient suffers from anemia, Thrombocytopenia and renal failure. The strain responsible for HUS is EHEC O157: H7.

The Pilli present on the surface of Ecoli Bind to the intestinal epithelial cells and the shiga like toxin is released. This in turn inhibits the 60s ribosomes and thus the intestinal cells die due to which bloddy diarrhea results with abdominal cramps. This resembles the diarrhea caused by shigella thus the name shiga like toxin.

3.      Enteroinvasive E.coli:

The bacteria invades the cells and release shiga like toxin. This in turn causes an immune mediated inflammatory response which results in wbcs invading the cells and causing bloody diarrhea and also it causes fever.

E.coli UTI:

Pilli allows E.coli to travel up the urethra and infect the bladder (cystitis), the bacteria then moves further up to infect the kidney (pylonephritis). Commonly this happens in catheterized patients.

Symptoms: dysuria, increased urinary frequency, fullness over the bladder.

E.coli Meningitis:

Commonly occurs during the first month of life . Transmitted through the birth canal.

Diagnosis: blood and CSF cultures.

E.coli Sepsis:

Septic shock due to lipid A component of LPS. It can be diagnosed through blood culture.