Lecture 5 - Ecoli 0157 Flashcards
Where doe ecoli fall phylogenetically
Proteobacteria gamma
Name some general characteristics of enterobacteriaceae
- gram - Straight rods Motile (Peritrichous) or non motile Non sporulating Facultative anaerobes Production of acid from glucose Catalase positive oxidase negative
Name some major genera of enterobacteriaceae
Escherichia Salmonella Shigella Citrobacter Proteus
Who noticed e coli in diarrhoea ofchildren
theodore Erlich
Name general characteristics of Ecoli
Gram - Facultative anaerobe Non spiorulating Peritrichous Growth - temp 10-55 . O 37 deg PH 4.5-9. O 7-7.5 Aw 0.96 (7% Nacl)
Why doesnt e coli satisfy Koch postulates
Both in healthy and diseased organism
Where does e coli live
Commensal - human and warm blooded animals eg, cattle
How quickly does e coli colonise gut
Babies almost pure culture - one of first organisms to colonise gut from mother
Once take in food this reduce as get more organisms
Main groups of pathogenic e coli
Enteropathogenic ecoli (EPEC) - infantile diarrhoea (adults immune)
Enterotoxigenic (ETEC) - on holiday e.g Egypt. Endemic population usually resistant
Enteroinvasive (EIEC) - produce symptoms similar to dysentery
Enterohaemmorhagic (EHEC) - verocytotoxin ecoli (VTEC/STEC) 0157 model strain
What is ETEC associated with
Ice salad
Travel
Why is enteroinvasive like shigella dysentery
Invasive ecoli penetrate through gut wall and into peritoneum so gut come troug hole created into faeces and out
Red blood in faeces
Where as EHEC first isolated
Canada
How is EHEC different to other types of ecoli
Non invasive like EIEC
Not produce enterotoxin like ETEC
Clinically different to EPEC
What are main serogroups for EHEC
Big 5 - 026, 0103, 011, O157
What caused it be recognised as foodborne pathogen
Jack in a box outbreak - chain of burger restaurants in US. Ask for burger to be poked how wanted it to be done
Who made concept of serotyping
Kauffmann White
What is O157
Antibody reaction with LPS on cell wall - antigenically distinct
Antibody 157 recognise antigen 157 which is certain configuration of sugars and lipids on outer cell wall
How many possibility are there for O and H antigens
173 o antigen
55 possibilities of H - flagella
Why are 0157 not all vtec
- vtec can be not 0157 r.g. O26
- some 0157 don’t produce toxin
NOT ALL INTERCHANGABLE
What are risk factors for ecoli 0157
Assumptomatic carrier.- cattle
Vehicles - food - MILK (unpasteurised) and vegetables grown in faeces and eating meat directly risk
Person to person - when symptomatic shed massiv number in own faeces- large congregation of people, e,g. Nursery, swimming etc
Contact animals - open farms - young children exposrd via faeces on fence etc
What is main annual case of 0157 in uk
900 and 1000 cases
What country has most e coli cases
Scotland unknown why
What are symptoms of EHEC
- could get diarrhoea disease (nicest option)
If get worse can get Haemoragic colitis - haemmoraghing of colom - blood in faeces - 10% of children under 5 or 6 cab get haemolytic ureamic syndrome = most susceptible cause complications of kidney - lead to kidney failure. Not well to treat so either need dialysis or transplant
- older patients can get thrombotic thrombocytopaenic pupura (TTP) - blood clots, bruising and internal bleeding as result of toxin mopping up plateletsa
What is duration of EHEC 0157
2-9days
What is infectious dose of VTec0157
<100 organisms (possibly one organism!!!!)
What is 0157 mildly resistant to
Acid and drying
- got to get through stomach acid so mild resistance get it through to establish infection in small intestine
What is 1057 attachment mechanism
Peristalsis of stomach fierce for small organisms - need to attach
Fimbral- OMP?
Similar to EPEC bfp
- type iV fimbrae (bundle forming pili)
Must be chromosomal encoded
If we knock fimbrae out of which type of ecoli do they lose pathogenicity
ETEC fimbrae
Dont kno how 0157 does it
What is A/E lesion
Where ecoli bind in clumps together - specific binding areas
(Attachement and effacement lesions (AE))
Localised adherence to HEP2 cell s
Why do we see AE lesions
Locus of enterocyte effacement (LEE) or pathogenicity island
Bacteria obtain dna via horizontal gene transfer
Pathogenicity island that has been acquired by ecoli codes for 3 key things;
- intimin - 97KDa - chromosomal eae gene (intimate binding)
_ type III secretion method - EspA,B, D
- Translocated intimin receptor - Tir
Where is intimin expressed
SURFACE OF BACTIERUM
WHERE IS TIR
On top of pedestal gut cell
Analogy for intimin for tir
Get receptor translocated into cell (TIR) get molecule want to bind with ad then it fits
E.g. Have lock put own lock on box and to fit key. Pout key in an it unlocks
Hat is a type III secretion system
- syringe like delivery of molecules so pump out TIR that preset itself in surface of human cell - so now it already there so bacteria can bind
What does TIR polymerise
Actin - make whole underneath of human gut cell rise up as pedestal
When do ecoli begin to produce toxins
Once intimately bound via intimin and TIR
Why are toxins called very cytotoxins
Killed Africa green monkey kidney cells. Kidney cells express receptor for toxins
What are the toxin
VT1 and VT2
Antigenically distinct VT1 and VT2. VT2 have subtypes VT2a, VT2b, Vt2c etc up to approx G
What is the receptor toxins look for on kidney etc cell
Globotriasylceramide (Gb3) receptor
Found particularly on surface of kidney cells hence HUS disease
What does it mean by it being a compound toxin
A and B subunit toxin
A subunit (active part) B binding part - got to Gb3 receptor
What does a subunit of toxin do
Prevent initiation of protein synthesis by binding to tRNA to cleave particular bond on 28s subunit of ribosomal RNA
inhibit peptide chain elongation so lead to cell death
What is K 12
Non pathogenic e coli
Approx how many genes have e coli 0157 acquired as O islands to make it very pathogenic (that their ecoli dont have)
1387 genes
How did e. 0157 get these O islands pathogenic genes
PUNCTUATED EVOLUTION
Learnt toxin, receptor binding, delivering toxin - gaining genes via pathogenicity island
How do we detect sorbitol MacConkey
Organism ferment sugar - create acid - acid react wth pH indicator and get RED colonies
E coli cant ferment sugar alcohol sorbitol so it doesnt produce acid so colonies stay WHITE
White show VTEC 0157
How do we treat and orevent EHEC 0157
- treatment
Self limiting, rehydration
Antibiotics therapy NO WAY - if give amoxicillin can make situation worse as organism upregulate toxin. Cannot give antibiotics
PREVENT
- avoid risk factors - undercooked meat. Contact with animals. Good hygiene.
