Lecture 10- Escherchia coli Flashcards
E.coli
- gram negative, motile, nonsporulating, rod-shaped, and a facultative anaerobe
- part of the normal microbial population of the intestine track of humans, and other warm blooded animals
Why can E.coli be used as an indicator for fecal contamination?
-E.coli is found in the large intestine in the millions of cells per gram
What determines the phenotype and disease caused by each phenotype of E.coli?
virulence factors they pick up via horizontal gene transfer determines which phenotype they get
Enteropathogenic E.coli (EPEC)
- has the ability to form distinctive lesions on the surfaces of intestinal epithelial cells
- Locus of enterocyte effacement (LEE) genes
- generally does not have enterotoxins
Which group does EPEC effect the most?
-children in developing countries
How is EPEC transmitted?
Fecal-oral route, humans are the only identified carrier
How do you prevent transmission of EPEC?
-follow proper hygiene methods, have clean fresh water supplies
How does EPEC cause diarrhea?
- effacement of microvilli may lead to a decrease in absorptive surfaces thereby contributing to diarrhea by increasing water in the small intestine
- tight junction may be disrupted leading to increased intestinal permeability
Shiga toxin producing E.coli (STEC)
- presence of Shiga toxin 1 or 2 which is acquired by bacteriophage infection
- has LEE genes and forms lesions on the microvili
What is the most common serotype of STEC?
O157:H7
How is STEC transmitted?
Via fecal oral rout
Cattle are major reservoir for STEC
Infectious dose is very low
What symptoms can STEC cause?
- mild to bloody diarrhea
- Haemolytic uremic syndrome (HUS)
What is Haemolytic uremic syndrome (HUS)?
-caused by the destruction of RBC. The damaged RBC clog the filtering system in the kidneys which can lead to life-threatening kidney failure.
Are antibiotics recommended for STEC?
-No, because antibiotics cause stress and therefore forces the strain to leave the E.coli and invade another E.coli
Enteroinvasice E.coli/ Shigella (EIEC)
- facultative intracellular pathogens
- invasive and divide in the intracellular milieu of intestinal cells
How does the infection process work for EIEC?
- cells penetrate the epithelial barrier, induce macrophage cell death, invade intestinal epithelial cells, engagement in intra- and intercellular movement, and degrade epithelial integrity
- destabilize the epithelial tight junctions and induce epithelial cell death
What is the inflammatory response to the infection caused by EIEC?
-apoptotic macrophage and IEC invasion perforates the epithelial barrie and leads to tissue lesions
Do EIEC and Shigella have the same virulence strategies?
-yes but Shigella has increased virulence
What are the symptoms of EIEC/Shigella?
- mild watery diarrhea, fatigue, malaise, fever, anorexia
- later in the disease there may be abdominal cramps, blood, mucus in diarrhea and dehydration
- usually self-limiting
- HUS may happen from Stx toxin
What are the treatments for EIEC/ Shigella
- oral rehydration
- antibiotics shorten the duration of illness, unlike STEC, antibiotics seem to protect against HUS
- Antibiotic resistance is high
What is Enteroaggregative E.coli (EAEC) known for?
- most common bacterial pathogen identified in patients with diarrhea
- causes persistent diarrhea in children, immunocompromised patients
How is EAEC transmitted?
food and water contaminated with fecal material
-found in calves, piglets, horses
What is the three part infection model of EAEC?
- cells adhere to intestinal mucosa
- cells produce enterotoxins and cytotoxins
- the mucosa becomes inflamed due to toxins and the immune system (diarrhea)
Which E.coli is the only one to have a heat-stable toxin?
Enterotoxigenic E.coli (ETEC)
-heat-stable toxin acts by inducing chloride and fluid secretion into the lumen
