Vtec Flashcards
Intro
> 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
Common strains
O157:H7
O26
O104:H4
Emergence of o157:h7
Initial outbreak of o157:h7 in 1982 in undercooked burgers
Evolution
First in an
Acquired stx toxin first
Then the o157 plasmid encoding a haemolysin
Lost ability to ferment b glucuronidase and sorbitol
Super shedders
Greater than 10^4 cfu/g
Colonised at recto anal junction
Sources
Both o157 and non o157 found in ruminants
Virulence factors
Locus of enterocyte effacement
Plasmid o157
Shigatoxins
Lee
A pathogenicity island
41 different genes responsible for attaching and effacing lesions
Encodes a type iii secretion system
Associated with disease but not essential
Types iii secretion system, what does it eject
Injects effector molecules across host cell membrane
Needs contact with membrane though
Secretes TIR receptors into host cell
TIR receptors
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
What follows tir insertion into mrmbrane
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
Po157 plasmid
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
What carries stx
Lambdoid prophages
Trends/mortality of hus
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
What strain predominates in hus in ireland
50% we’re o157
33% o26
5/6 ‘big 6’ non o157s involved
Majority were stx2 only
How much more likely is hus to developing, stx2 vs stx2
Stx2 is x4 times more likely
Resistance in 0157
Sulfonamide and tetracycline common in o157
Esbls TEM/CTXM in Denmark
0104 resistance
Ampicillin, cefotaxime, ceftazidime, streptomycin and tetracycline resistance
Toxin binding
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
How does A2 work
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
Why is stx2 a worse prognosis
More frequently associated with hus and haemorrhagic colitis
Aldo cause thrombosis microangiopathy -> thrombocytopenia and haemolytic anaemia
How does o104 virulence factors differ
Missing o157 plasmid
Missing LEE
Has AAF instead -> better adhesion
Stx transfered via phage
Biofilm production
Esbl production
What % progress to hus
90% recover, hus progress
About 5% of hus result in death, 60% recover
Only about 2% of non0157 progress to hus
EAHEC stands for? What strain does it refer to? What was the original outbreak?
Enteroadherant haemorrhagic e.coli
O104:H4
Sprouts in Germany
- 4000 cases and 53 deaths
