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MICROBIOLOGY II > Lecture 5 - Ecoli 0157 > Flashcards

Lecture 5 - Ecoli 0157 Flashcards

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1
Q

Where doe ecoli fall phylogenetically

A

Proteobacteria gamma

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2
Q

Name some general characteristics of enterobacteriaceae

A 
- gram - 
Straight rods 
Motile (Peritrichous) or non motile 
Non sporulating
Facultative anaerobes 
Production of acid from glucose 
Catalase positive oxidase negative
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3
Q

Name some major genera of enterobacteriaceae

A 
Escherichia 
Salmonella 
Shigella 
Citrobacter
Proteus
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4
Q

Who noticed e coli in diarrhoea ofchildren

A

theodore Erlich

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5
Q

Name general characteristics of Ecoli

A 
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)
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6
Q

Why doesnt e coli satisfy Koch postulates

A

Both in healthy and diseased organism

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7
Q

Where does e coli live

A

Commensal - human and warm blooded animals eg, cattle

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8
Q

How quickly does e coli colonise gut

A

Babies almost pure culture - one of first organisms to colonise gut from mother

Once take in food this reduce as get more organisms

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9
Q

Main groups of pathogenic e coli

A

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

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10
Q

What is ETEC associated with

A

Ice salad

Travel

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11
Q

Why is enteroinvasive like shigella dysentery

A

Invasive ecoli penetrate through gut wall and into peritoneum so gut come troug hole created into faeces and out

Red blood in faeces

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12
Q

Where as EHEC first isolated

A

Canada

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13
Q

How is EHEC different to other types of ecoli

A

Non invasive like EIEC
Not produce enterotoxin like ETEC
Clinically different to EPEC

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14
Q

What are main serogroups for EHEC

A

Big 5 - 026, 0103, 011, O157

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15
Q

What caused it be recognised as foodborne pathogen

A

Jack in a box outbreak - chain of burger restaurants in US. Ask for burger to be poked how wanted it to be done

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16
Q

Who made concept of serotyping

A

Kauffmann White

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17
Q

What is O157

A

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

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18
Q

How many possibility are there for O and H antigens

A

173 o antigen

55 possibilities of H - flagella

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19
Q

Why are 0157 not all vtec

A
  • vtec can be not 0157 r.g. O26
  • some 0157 don’t produce toxin

NOT ALL INTERCHANGABLE

20
Q

What are risk factors for ecoli 0157

A

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

21
Q

What is main annual case of 0157 in uk

A

900 and 1000 cases

22
Q

What country has most e coli cases

A

Scotland unknown why

23
Q

What are symptoms of EHEC

A
  • 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
24
Q

What is duration of EHEC 0157

A

2-9days

25
Q

What is infectious dose of VTec0157

A

<100 organisms (possibly one organism!!!!)

26
Q

What is 0157 mildly resistant to

A

Acid and drying

- got to get through stomach acid so mild resistance get it through to establish infection in small intestine

27
Q

What is 1057 attachment mechanism

Peristalsis of stomach fierce for small organisms - need to attach

A

Fimbral- OMP?
Similar to EPEC bfp
- type iV fimbrae (bundle forming pili)
Must be chromosomal encoded

28
Q

If we knock fimbrae out of which type of ecoli do they lose pathogenicity

A

ETEC fimbrae

Dont kno how 0157 does it

29
Q

What is A/E lesion

A

Where ecoli bind in clumps together - specific binding areas
(Attachement and effacement lesions (AE))

Localised adherence to HEP2 cell s

30
Q

Why do we see AE lesions

A

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

31
Q

Where is intimin expressed

A

SURFACE OF BACTIERUM

32
Q

WHERE IS TIR

A

On top of pedestal gut cell

33
Q

Analogy for intimin for tir

A

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

34
Q

Hat is a type III secretion system

A
  • 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
35
Q

What does TIR polymerise

A

Actin - make whole underneath of human gut cell rise up as pedestal

36
Q

When do ecoli begin to produce toxins

A

Once intimately bound via intimin and TIR

37
Q

Why are toxins called very cytotoxins

A

Killed Africa green monkey kidney cells. Kidney cells express receptor for toxins

38
Q

What are the toxin

A

VT1 and VT2

Antigenically distinct VT1 and VT2. VT2 have subtypes VT2a, VT2b, Vt2c etc up to approx G

39
Q

What is the receptor toxins look for on kidney etc cell

A

Globotriasylceramide (Gb3) receptor

Found particularly on surface of kidney cells hence HUS disease

40
Q

What does it mean by it being a compound toxin

A

A and B subunit toxin

A subunit (active part) 
B binding part - got to Gb3 receptor
41
Q

What does a subunit of toxin do

A

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

42
Q

What is K 12

A

Non pathogenic e coli

43
Q

Approx how many genes have e coli 0157 acquired as O islands to make it very pathogenic (that their ecoli dont have)

A

1387 genes

44
Q

How did e. 0157 get these O islands pathogenic genes

A

PUNCTUATED EVOLUTION

Learnt toxin, receptor binding, delivering toxin - gaining genes via pathogenicity island

45
Q

How do we detect sorbitol MacConkey

A

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

46
Q

How do we treat and orevent EHEC 0157

A
  • 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.

MICROBIOLOGY II (9 decks)

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