Escherichia coli Flashcards
Summarise E.coli (and it’s pathogenicity).
e.g. E. coli = NOT always pathogenic
= gram negative, facultative anaerobic + non-sporulating, rod-shaped
= can live on wide variety of substrates mixed-acid fermentation in anaerobic conditions (ideal for lower gut)
= optimal growth = 37 oC
= strains that possess flagella are motile, mostly peritrichous
= possess ability to transfer DNA via bacterial conjugation, transduction, or transformation
(genetic material can spread horizontally through an existing population)
Info about normal
distribution of E.coli?
large population
= genetic and phenotypic diversity
many strains
= (sub-groups with unique characteristics - e.g. molecular level, growth differences)
= allows the source of faecal contamination to be determined
= can benefit hosts (produce vitamin K2, B12)
= prevent establishment of pathogenic bacteria within intestine
normally
= 0.1% of gut flora
= colonises infant’s GI tract within 40 hours of birth
= in bowel, adhered to mucus of large intestine
remain commensal
= as long as bacteria do not acquire genetic elements encoding for virulence factors
What are results of pathogenic E. coli?
Causes in humans:
= gastroenteritis
= UTIs
= neonatal meningitis
Rarer cases:
= haemolytic-uremic syndrome (HUS)
= peritonitis (peritoneum)
= mastitis
= speticeamia
= gram-negative pneumonia
What are examples of virulence determinants of pathogenic E.coli?
Adhesins
= fimbriae
= EPEC adherence factor
Invasins
= haemolysin
= shigella-like invasins
Motility / chemotaxis
= flagella
Toxins
= endotoxin (LPS)
= siderophores
= LT / ST toxin
Antiphagocytic surface properties
= capsules
= K antigen
= LPS
Defence against serum bactericidal reactions
= LPS
= K antigens
Defense against immune responses
= capsules
= K antigens
= LPS
What is pathogenic E.coli?
= E. coli that have acquired virulence genes
(six recognised categories of diarrhoeagenic E. coli with unique features in interaction with eukaryotic cells)
Over 700 antigenic types (serotypes) of E. coli recognised
= based on O, H and K antigens
O = part of lipopolysaccharide layer
K = capsule
H = flagellin
(whip-like structure, locomotion, sensory perception, pathogenicity)
(20 structural proteins form basal body, hook, filament)
(3 sub domains: N-termini, C-termini, variable region)
F = MR fimbriae (rare)
(shorter than flagellae)
(enhances ability for bacteria to attach to host and cause disease)
e.g. Escherichia coli O157:H7
ALL elicit immune response in animals
What are the classes of pathogenic E. coli?
EPEC
= EnteroPathogenic E. coli
= watery diarrhoea and vomiting
= Bfp, Intimin, LEE
EHEC
= EnteroHaemorrhagic E.coli
= Bloody diarrhoea
= Shiga toxins, Intimin, Bfp
ETEC
= EnteroToxigenic E. coli
= Watery diarrhoea and vomiting
= Heat-labile and sheat-stable toxins, CFAs
EAEC
= EnteroAggregative E.coli
= Diarrhoea with mucus and vomiting
= AAFs, cytotoxins
DAEC
= Diffusely Adherent E. coli
= Watery diarrhoea recurring UTI
= Daa, AIDA
EIEC
= EnteroInvasive E. coli
= Watery diarrhoea and dysentry
= Shiga toxin, haemolysin, cellular invasion, Ipa
What is EPEC?
= EnteroPathogenic E. coli
= adhere to small bowel enterocytes
= destroy normal microvillar architecture (attaching and effacing lesion)
= cytoskeletal derangements accompanied by inflammatory response and diarrhoea
- initial adhesion
- protein translocation by type III secretion
- pedestal formation
What is EHEC?
= EnteroHaemorrhagic E.coli
= induces attaching an effacing lesion in the colon
= same as EPEC + elaboration of Shiga toxin
= systemic absorption of which leads to potentially life-threatening complications
What is ETEC?
= EnteroToxigenic E. coli
= adhere to small bowel enterocytes (like EHEC)
= induces watery diarrhoea by secretion of heat-labile (LT) / heat-stable (ST) enterotoxins
What is EAEC?
= EnteroAggregative E.coli
= adheres to small and large bowel epithelia in a thick biofilm
= elaborates secretory enterotoxins and cytotoxins
What is DAEC?
= Diffusely Adherent E. coli
= elicits signal transduction effect in small bowel enterocytes
= manifests as growth of long finger-like cellular projections, which wrap around the bacteria
What is EIEC?
= EnteroInvasive E. coli
= E. coli O157:H7
= invades colonic epithelial cells
= lyses the phagosome
= moves through cell by nucleating actin microfilaments
= bacteria might move laterally through the epithelium by direct cell-to-cell spread or might exit and re-enter the baso-lateral plasma membrane
= NOT normally found in human intestinal flora
= can be spread from ruminants to humans
(undercooked meats, unpasteurised milk, contaminated water, petting zoos, contaminated fields = produce)
What is the model of pathogenesis induced by EIEC?
= invades epithelium from intestinal lumen through M-cells
= phagocytosed by resident macrophages
= escape phagosome + replicate in epithelial cells
= induce apoptosis in macrophages
= bacteria released
(invade epithelial cells from basolateral side, move into cytoplasm by triggering actin polymerisation, spread to adjacent cells)
= genes necessary for invasion carried 140-MDa plasmid
= have mxi and spa loci (encode type III secretion apparatus - T3SSs)
= T3SSs are central virulence factors, inject protein effectors of virulence into eukaryotic host cells
= IpaA - IpaD = secreted protein, acts on host cell = causing actin rearrangement and membrane ruffling = bacterial internalisation
= once inside cell vacuole = IpaB protein degrades vacuole = release bacteria into cytosol
= outer membrane protein (VirG) triggers actin polymerisation by binding cytosol components = propels organisms through cell into neighbouring cells
= expression of virulence genes is transcriptionally regulated by VirR gene (affected by temperature)
= bacteria are invasive at 37 oC , non-invasive at 30oC
What is the pathophysiology of E. coli O157:H7?
= Organism swallowed and moves through GI tract, adheres to mucosa and colonises
= becomes resistant + tolerant to stomach acid then proliferates
= body reacts with watery and bloody diarrhoea to flush bacterium out of body
= shiga toxins enter bloodstream and begin translocation = damage kidneys
What are the signs and symptoms of E. coli O157:H7 infection?
Definite:
= bloody diarrhoea
= vomiting
Potential
= no or low fever
= haemolytic uremic syndrome (HUS)
= thrombotic thrombocytopenic purpura (TTP)
