Lecture 1 - Revision Flashcards
Microbial pathogens overview
- 16 million die from infectious disease/year
- 1 in 12 have viral hepatitis
- 50M new chlamydial cases per year
- Clostridium botulinum toxin - 400g could kill population
1400 known species of microbial pathogens
human pathogens: 1% of total microbe species on planet
An overview of Escherichia coli
- Gram-negative, facultative anaerobic and non-sporulating
- rod-shaped (2x0.5um)
- cell volume is 0.6-0.7um3
- Live on wide variety of substrates - mixed acid fermentation in anaerobic conditions - ideal for lower gut
- 37 degrees optimal growth, some ok at 49 degrees
- Strains with flagella are motile. Mostly peritrichous
Facts surrounding E. coli
- High degree of genetic and phenotypic diversity (only 20% genome common to all strains).
- Many strains (phylotype) - Sub-groups which distinguishable characteristics
- Typically host-specific, possible to determine faecal contamination in environmental samples
- Strains part of normal flora - can produce vitamins B12 and K2, prevent establishment of pathogenic bacteria in gut
- 0.1% gut flora
- colonizes in infant’s gastrointestinal tract after 40 hours, arrive with food/water, or handling
- Adhere to mucus in large intestine
- Commensal as long as no genetic elements encoding for virulence factors
What diseases can E. coli cause
Gastroenteritis
UTIs
Neonatal meningitis
Rarer:
HUS, septicaemia, Gram-negative pneumonia
Classification of Pathogenic E. coli
> 700 serotypes of E. coli based on:
O-antigen - part of lipopolysaccharide layer
K antigen - Capsule
H-antigen - flagellin
F-antigen - MR fimbriae
Main example: O157:H7
H-antigen
Whip-like structure for locomotion, perception and pathogenicity (motility, adhesion, secretion of virulence factors)
Basal body, hook and filament formed from >20 distinct proteins
Bacterial flagellin proteins divided into three subdomains: N, C and middle variable region
- Variable domain antigenically diverse - exploited for identification
What is a pathogenic E. coli
E. coli that have acquired virulence genes
Six recognised diarrhoeagenic E. coli - Each with unique features in eukaryote interaction
EPEC - EnteroPathogenic E. coli
Adhere to small bowel enterocytes
Destroy microvillar architecture
Cytoskeletal cellular derangements accompanied by inflammation and diarrhoea - Initial adhesion
- Protein translocation by type III secretion, bundle-forming pili forms
- pedestal formation
EHEC
- Enterohaemorrhagic EC induce attaching and effacing lesion, but in colon
- Shiga toxin secreted
- Systemic absorption
- Life-threatening complication
- Inflammation and diarrhoea
Enterotoxigenic E. coli
Similar to EHEC but adheres small bowel enterocytes
Watery diarrhoea induced by heat-liable ( gangliosides GM1, GD1b) and/or heat-stable (guanylate cyclase) enterotoxin secretion
Bacteria bind via CFA or colonization factor antigen
EAEC
EnteroAggressive E. coli
Adheres small and large bowel apithelia in thick biofilm
Releases entero and cytotoxins
- Biofilm forms attached by aggregative adherence fimbriae
- Cytotoxins and enterotoxins released into cell e.g. Shigella enterotoxins, ST enterotoxins, serine proteases, plasmid encoded toxin
Diffusely adherent E. coli
Characteristic signal transduction effect in small bowel enterocytes
Manifests as growth of long finger like cell cellular projections which wrap around bacteria
DAF and F1845 allow bacteria to bind
EIEC
EnteroInvasive E. coli
Invade colonic epithelial cells:
- Lyse phagosome
- Move through cell by nucleating actin microfilaments
Bacteria can move through epithelium through direct cell-to-cell spread
May leave and re-enter through baso-lateral plasma membrane
Pathogenesis model of EIEC
EIEC invade epithelium from intestinal lumen by M-cells
Invade epithelial cells and phagocytosed by resident macrophages
- Escape through phagosome and replicate in epithelial cells - induce macrophage apoptosis
- Bacteria may: invade epithelial cells from baso-lateral side, move into cytoplasm by actin polymerization, spread to adjacent cells
mxi and spa genes in 140MDa plnv plasmid carried by EIEC have type III secretion systems and inject protein effectors of virulence in eukaryotes
IpaA and IpaD (secreted proteins) cause actin rearrangement and membrane ruffling causing bacterial internalization
IpaB degrades vacuole to release bacteria into cytosol
Outer-membrane protein VirG triggers actin polymerization by binding cytosol components - propels organism to neighbouring cells
VirR gene controls virulence gene expression:
- Chromosomally encoded
- Temperature affected
O157:H7 EHEC
- Causes bloody diarrhoea and no fever
- Causes Hemolytic-uremic syndrome (HUS) and kidney failure
- Has bacterial fimbriae for attachment (e. coli common pilus)
- Moderately invasive, and possesses a phage-encoded shiga toxin - elicits immune response
EHEC can verocytotoxin E. coli or shiga-like toxin E. coli
Scouts
In May 2000, scouts went on a camping field trip in Aberdeenshire, Scotland
Before this, 300 sheep/lambs were grazing in the field for 6 days
337 people went, including 104 adults and 223 scouts
The trip later got cancelled due to heavy rainfall
20 people later got ill from O157 E. coli infection, and there was no evidence it was the food
Caused by hand-to-mouth or hand-to-food-to-mouth transmission caused by touching the soil
Animals were asymptomatic
E. coli found on tents, climbing equipment, soil, clothing, footwear etc
O157:H7 can survive in soil for 15 weeks
Church lunch
- Broken heater
- No temp probes to check temp of cooked meat
- Staff poorly strained
- No quick cooling of meat
- Meat was infected with O157:H7, causing 45 infections and 8 deaths from incorrectly cooked stewed beef
Residential home
1st butcher sold 2nd butcher infected turkey meat which they then sold to a residential home for sandwiches causing 5 deaths
Germany, 2011
E. coli O104:H4 outbreak
Thought to be EHEC, but more specifically STEC
Bean sprouts, cucumbers, fenugreek
3950 cases with 54 deaths
845 got HUS
Strain was typed as enteroaggregative Shiga-toxin producing E. coli O104:H4 producing extended-spectrum beta-lactamase
NOT EHEC
E. coli STEC/VTEC
4 different cheeses
30 cases/1 fatality
