Enterotoxigenic and Enteroaggregative E.coli Flashcards
Explain the E.coli classification system
- Similar to Kauffman White system
- Based on highly variable surface antigens interacting with specific antibodies
- Searches for:
○ ‘O’ somatic antigen
○ ‘H’ flagella natigen
○ ‘K’ capsular antigen - This forms the basis of serogrouping/serotyping
How are E.coli pathotypes based? What are the major pathotypes?
- Based on the presence of different virulence factors
- Major pathotypes:
○ UPEC: uropathogenic
○ NMEC: Neonatal meningitis
○ Diarrheagenic E.coli
§ EIEC: enteroinvasive
§ EPEC: Enteropathogenic
§ EHEC: Enterohaemorrhagic
§ DAEC: Diffusely adhering
§ ETEC: Enterotoxigenic
§ EAEC: Enteroaggregative
How is the pathogenicity of E.coli established?
Through plasmids and phages
Explain where ETEC infections occur, the type of disease it causes, and what group of people it infects predominantly
- Occurs In small intestine
- Causes diarrhea
- Infect children <5 and people visiting developing countries
What are the major virulence factors of ETEC?
- Adhesion
- Heat labile toxins (LT)
- Heat stable toxins (ST)
How do ETEC establish adhesion?
- Type 1 Fimbriae
What are Colonization factors? (ETEC)
- Factors which determine the type of adhesion
- Create a broad range of fimbriae/pili (25)
Explain the structure of CFAI-CFAIV (ETEC)
- CFAI - long and rigid
- CFAII - thin and flexible
- CFA III - bundle forming, long and flexible
- CFAIV - extremely long pilus
How is CFA expression regulated? (ETEC)
- Genes encoding CFA frequently encoded on plasmids
- When there is low iron, production of CFA increases
- When there is excess iron, production of CFA decreases
- cfaD is master regulatory and also responds to bicarbonate
How does ETEC cause diarrhea?
By releasing enterotoxins
Explain the structure and the mechanism of action of Heat labile toxins (LT) (ETEC)
- LT: 2 forms, LT-1 and LT-II
- Structurally, antigenically and functionally related to cholera toxin
- Increases Cellular cAMP leading to reduced water absorption (ADP ribosylating toxin)
○ AB5 toxin (a peptide in middle, 5 binding peptides surrounding it)
○ Attach to host GM1 ganglioside receptor in lipid rafts
○ A protein brought closer to host surface and internalized into host cell
○ Once inside, A protein breaks into 2 subunits and A1 subunit is activated
○ A1 subunit hydrolyses NAD -> A1-ADP-Ribose + Nicotinamide
○ A1 uses ADP-ribose to ribosylate Gsa which creates GDP and shifts ATP to cAMP, activating cAMP dependent protein kinase A
○ Protein kinase A activates cystic fibrosis transmembreane conductance regulator (CFTR chloride channel) which leads to increased chlorice ion secretion, decreased uptake of NaCl through inhibition and leads to ion imbalence which causes fluid loss due to osmotic pressure
Explain the structure and mechanism of action of Heat stable toxins (ST) (ETEC)
- ST structurally distinct from LT
○ Small cysteine-rich peptide
○ Mimic human signaling peptide
§ Uroguanylin
§ Guanylin
○ ST binds to Guanylyl cyclas C receptor located in the apical membrane of host cell
○ Guanylyl cyclas regulated intracellular cGMP
○ ST leads to increase in cGMP which activates PKG and phosphorylates CFTR leading to loss of fluid
What are Postulated secondary effects of LT? (ETEC)
- LT appears to modulate innate immune system
- Modulate adherence of ETEC
- Decrease release of antimicrobial peptides
What is the difference between toxigenic infection and invasion? (ETEC)
- Toxigenic infection is when bacteria is on the outside of the cell and toxins are used to disrupt normal function
- Invasion is when bacteria enters cell and destroys it
How do you diagnose ETEC diseases?
- ETEC strains usually not routinely characterized in diagnostic labs
- Diagnosis based on identification of LT and ST in stool smaples
○ Immunological means -> ELISA
○ Multiplex PCR for LT and ST
