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4.2 Medical Microbiology > Vtec > Flashcards

Vtec Flashcards

1
Q

Intro

A

> 400 e.coli serotypes that harbour stx genes
Classed on O,H,K antigens
Virulence differs between strains
Stx2 is 1000 times stronger then stx1
Foodborne illness - cattle
Bloody diarrhea, hus, haemorrhagic colitis

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2
Q

Common strains

A

O157:H7
O26
O104:H4

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3
Q

Emergence of o157:h7

A

Initial outbreak of o157:h7 in 1982 in undercooked burgers

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4
Q

Evolution

A

First in an
Acquired stx toxin first
Then the o157 plasmid encoding a haemolysin
Lost ability to ferment b glucuronidase and sorbitol

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5
Q

Super shedders

A

Greater than 10^4 cfu/g
Colonised at recto anal junction

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6
Q

Sources

A

Both o157 and non o157 found in ruminants

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7
Q

Virulence factors

A

Locus of enterocyte effacement
Plasmid o157
Shigatoxins

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8
Q

Lee

A

A pathogenicity island
41 different genes responsible for attaching and effacing lesions
Encodes a type iii secretion system
Associated with disease but not essential

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9
Q

Types iii secretion system, what does it eject

A

Injects effector molecules across host cell membrane
Needs contact with membrane though
Secretes TIR receptors into host cell

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10
Q

TIR receptors

A

When in host cell - injected by TTSS - they undergo a tyrosine phosphorylation event

This modification allows the tirs to be inserted into the host membrane

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11
Q

What follows tir insertion into mrmbrane

A

Sn adhesion intimin (eae) can then bin to tir which attaches the bacteria to the host cell

We then get other secreted protein (EPS)

Polymerisation of actin molecules forms a pedestal

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12
Q

Po157 plasmid

A

An F like non conjugative plasmid
19 genes e.g
ehxA - Encode haemolysin A -> lysis of rbcs
TTSS - secretary system apparatus
KatP - encodes catalase peroxidase- protects damage from oxidative damage
esp1 -> serine protease -> micro vascular damage

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13
Q

What carries stx

A

Lambdoid prophages

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14
Q

Trends/mortality of hus

A

HUS most common in <5yrs old (15%) compared to 1.2% in adults

In one irish study 90% were in <15yr olds

Highest mortality in >60

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15
Q

What strain predominates in hus in ireland

A

50% we’re o157
33% o26

5/6 ‘big 6’ non o157s involved

Majority were stx2 only

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16
Q

How much more likely is hus to developing, stx2 vs stx2

A

Stx2 is x4 times more likely

17
Q

Resistance in 0157

A

Sulfonamide and tetracycline common in o157

Esbls TEM/CTXM in Denmark

18
Q

0104 resistance

A

Ampicillin, cefotaxime, ceftazidime, streptomycin and tetracycline resistance

19
Q

Toxin binding

A

A/b toxin
B subunit binds Gb3 receptors on host cells
Internalised by endocytosis
Complex transported through golgi

A subunit cleaved into A1 and A2

20
Q

How does A2 work

A

Targets 28s rRNA of 60s ribodomal subunit

Results in inhibition of protein synthesis and inhibition of elongation factor 1 which can lead to cell death

21
Q

Why is stx2 a worse prognosis

A

More frequently associated with hus and haemorrhagic colitis

Aldo cause thrombosis microangiopathy -> thrombocytopenia and haemolytic anaemia

22
Q

How does o104 virulence factors differ

A

Missing o157 plasmid
Missing LEE

Has AAF instead -> better adhesion
Stx transfered via phage
Biofilm production
Esbl production

23
Q

What % progress to hus

A

90% recover, hus progress

About 5% of hus result in death, 60% recover

Only about 2% of non0157 progress to hus

24
Q

EAHEC stands for? What strain does it refer to? What was the original outbreak?

A

Enteroadherant haemorrhagic e.coli

O104:H4

Sprouts in Germany
- 4000 cases and 53 deaths

25
Q

EAHEC has AAF instead of normal virulence factors, what does this stand for? How does it work?

A

Aggregation adherence factor

AAF pili encodes hy aagR results in aggregation and adherence fimbria
Stacked brick adherence
Unusual tight binding to epithelium allowing quicker delivery of toxin

26
Q

EAHEC epedimiology

A

Emerging pathogen but spreading globally
Caused sporadic infections first in Asia and across Europe
Endemic to central Africa

Not zoonotic - human transmission, possible water contamination

27
Q

Hus rate in 0104

A

22%

28
Q

What antibiotic is dangerous for vtec

A

Ciprofoxacin triggers continuous transcription of bacteripjage toxin

4.2 Medical Microbiology (20 decks)

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