Escherichia coli Flashcards
State two conditions majorly caused by E.coli.
Urinary Tract Infection
Neonatal meningitis and septicemia
State the general characteristics of E.coli.
- Gram negative rods
- Some strains are capsulated
- Motile by peritrichious flagella
- Lactose fermenters
- Some strains are haemolytic on blood agar
- Indole and methyl red positive
State the virulence factors of E.coli.
- Adhesins
- Intimin - associated with adhesion & effacement
- Outer membrane proteins
- Surface antigens and toxins
- O antigen-LPS 1
- K antigen-associated with capsule
- H antigen-associated with pili
- Fimbriae attaches to uroepithelial cells
- Exotoxins- haemolysins and enterotoxins
*Fimbriae
*P fimbriae: UTI
* CFA (Colonization Factor Antigen) fimbriae - associated with ETEC
- Endotoxin
- Aerobactin (a siderophore)
- Present in uropathogenic strains of E. coli
- Promoting intracellular iron accumulation for bacterial replication
- O and K polysaccharide antigens - protect from complement and phagocytič killing
State the diarrhogenic of E.coli (5marks).
Mnemonic: HAPTI
Enterohemorrhagic E. coli (EHEC)
Enteroaggregative E. coli (EAEC)
Enteropathogenic E. coli (EPEC)
Enterotoxigenic E. coli (ETEC)
Enteroinvasive E.coli (EIEC)
State the manifestations of Extraintestinal pathogenic E.coli (ExPEC)
- uropathogenic E. coli (UPEC)
- neonatal meningitis E. coli (NMEC)
- sepsis-associated E. coli (SEPEC)
Describe pathogenesis of EHEC.
Affects colon
Causes bloody diarrhoea
Most common cause of HUC (hemolytic uremic syndrome)
Describe pathogenesis of EAEC.
Causes acutelchronic watery diarrhoea in children and immunocompromised.
Adhere to epithelia in a stacked bricks pattern
Release toxins-inflammation caused
Describe pathogenesis of EPEC.
Attachment: Bacteria adhere to small intestine epithelial cells.
A/E Lesions: Formation of attaching and effacing lesions.
Microvillus Destruction: Loss of absorptive surface.
Outcome: Diarrhea, mainly in infants, occasionally in adults.
Describe pathogenesis of ETEC.
Cause: Traveler’s diarrhea, infant diarrhea in developing countries.
Colonization: Attaches to small bowel mucosa.
Toxins:
LT (Heat-labile toxin): Similar to cholera toxin (A+B subunits).
ST (Heat-stable toxin): Binds guanylate cyclase, ↑ cGMP.
Effect: Disrupts ion balance, leading to diarrhea.
State which diarrhogenic strains affect largelsmall bowel
Large bowel: EHEC and EIEC
Small bowel: ETEC and EPEC
Both: EAEC
Which Diarrhogenic strains present with bloody/watery diarrhoea?
All are watery except EHEC and EIEC
What does UPEC stand for?
Uropathogenic Escherichia coli
What are the common routes of UTI caused by UPEC?
- Ascending infection via the urethra
- Fecal bacteria spreading up to the bladder, kidneys, or prostate
- Descending infection via hematogenous route
What is NMEC, and what does it cause?
Neonatal Meningitis E. coli (NMEC) causes neonatal meningitis.
What antigen is associated with NMEC, and what is its function?
K1 capsular antigen – antiphagocytic and responsible for bacterial spreading.
What are the potential sources of NMEC?
Hospital staff, urogenital tract, and digestive tract.
How is E. coli diagnosed in the lab?
- Gram Stain: Gram-negative rods, ± pus cells
- Culture Conditions: 35-37°C, 18-24 hrs
- Media:
Blood Agar (BA) – some strains β-hemolytic
MacConkey – pink lactose fermenters colonies
CLED – yellow colonies (lactose fermenters)
What are the IMViC test results for E. coli?
Indole (+), Methyl Red (+), Voges-Proskauer (-), Citrate (-) (IMViC: ++–)
Which biochemical tests are positive for E. coli in the IMViC series?
Indole test (+) and Methyl Red test (+)
Which biochemical tests are negative for E. coli in the IMViC series?
Voges-Proskauer test (-) and Citrate utilization test (-)
