micro 6

Question 1

what is shiga toxin producing e.coli also known as?

Answer 1

•Verocytotoxin producing E. coli

Question 2

what is a subset of shiga toxin producing e.coli?

Answer 2

• A subset of these can be called EnterohemorrhagicE. coli (EHEC)
• All EHEC are STEC but not all STEC are EHEC

Question 3

how infectious is STEC?

Answer 3

• STEC infectious dose is low

* Believed to be <100 cells (some say <10)

Question 4

what are the two main variants of STEC?

Answer 4

2 main variants Stx1 andStx2

Question 5

are the STEC variants the same?

Answer 5

•Antigenically different but same mechanism of action

Question 6

what are the STEC variants used for?

Answer 6

Used as markers for identification (PCR/multiplex PCR

Question 7

what is STEC associated with?

Answer 7

Associated with hemorrhagic colitis and hemolytic-uremic syndrome.

Question 8

what was the first iscolated STEC?

Answer 8

E.coli 0157:H7

Question 9

how can E.coli 0157:H7 be spread?

Answer 9

• Major foodborne pathogen

* Can be spread person-person through faecal shedding

Question 10

what are STEC 0157 ?

Answer 10

refers to EC strains which are 0157 but not necessarily H7 variants

Question 11

what are shiga toxins and where are they most commonly found?

Answer 11

• Family of toxins that are most commonly found in Shigella dysenteriae and some STEC serotypes
• Extremely potent bacterial toxin

Question 12

what are the two units which shiga toxins are composed of?

Answer 12

• Comprised of 2 units

* A (1 copy)•B (5 identical copies)

Question 13

how does shiga toxin producing e.coli work?

Answer 13

1. Bacteria binds to cell surface a)Intimin protein
2. B subunit binds to glycolipic globotriaosylceamide (Gb3)
3. Internalised within an endosome
4. Transported to Golgi a)A1 subunit is cleaved from B pentamer
5. Inhibits protein synthesis
6. Cell death

Question 14

what was clostridioides difficile known as?

Answer 14

•Was originally Clostridium difficile•Technically renamed in 2016

Question 15

what is c. difficle known for?

Answer 15

One of the most important healthcare associated MDR pathogens- NOT TRAVLERS DIAHORREA

Question 16

does c. difficile form spores?

Answer 16

• It forms SPORES and is ANAEROBIC!!•Lets it resist disinfection
• Cant survive in oxygen

Question 17

what is a way of subdividing strains based on the 16S-23S intergenic spacer region?

Answer 17

C. diff ribotypes

Question 18

what strain of the c. difficle causes the most severe disease?

Answer 18

•027 ribotype causes more severe disease

Question 19

what are c. diff toxinotypes?

Answer 19

are a group of strains that have changes in the toxin A and B coding region
•Known as PaLoc(Pathogenicity locus)

Question 20

how are c. diff ribotypes and toxinotypes done?

Answer 20

•Done by looking at PCR restriction fragment length polymorphism

Question 21

which toxinotypes have small and large variations?

Answer 21

• Toxinotype III has small variations

* Toxinotype X and XVII have large deletions in tcdA

Question 22

are c. diff spores metabolically dormant?

Answer 22

yes-•Can resist disinfection and environmental stress

Question 23

what are the differnt layers of a C.diff spore?

Answer 23

•Core (A)•Contains supercoiled DNA bound with SASPs•Partially dehydrated•Contains up to 1M Ca-DPA

• Inner membrane(B)
• Permeability barrier against chemicals
• Germ Cell Wall (C)
• Becomes the cell wall after germination
• Cortex (D)•NAM modified →muramicacid-delta lactam
• Outer membrane (E) and spore coat (F)•Predominantly Glyoproteins
• Exosporium(G)•Plays a role in host pathogen interactions

Question 24

what effect do antibiotics have on c. diff?

Answer 24

• Use of broad spectrum antibiotics can disrupt normal microflora
• Removes competition allowing C. diff to grow

Question 25

how is c. diff associated infection treated?

Answer 25

* Infection usually treated with antibiotics•1 in 3 may have relapse * Type of antibiotic may have an influence

Question 26

how do c. diff germinate? and where?

Answer 26

C. diff spores have to enter the body and transit to an anaerobic environment •Shown to germinate in the small intestine

Question 27

what does c. diff require in order to germinate?

Answer 27

* Requires a “signal” in order to germinate * Primary bile salt taurocholate can induce germination (in vitro) * Other primary bile salts also able to cause germination * Secondary bile salts shown to inhibit C.diff

Question 28

what is the c. diff clinical spectrum and how is it graded?

Answer 28

* Asymptomatic carriage * Non-toxigenic forms of C. diff•Toxin neutralising antibodies * Diarrhoea•Watery diarrhoea ≥3 times a day•5-7 on Bristol stool chart * Colitis and pseudomembranous colitis•C.difftoxinsattack colon epithelial cells causing damage•Produces an inflammatory response * Toxic megacolon•About 0.4-3% of all C.diffcases•38-80% mortality•Characterised by highly dilated colon, bloating- most severe

Question 29

what are the two main toxin strains produced by c. difficile?

Answer 29

•TcdA(enterotoxin) and TcdB(cytotoxin)

Question 30

what do different strain of c. difficile do? A-D

Answer 30

A: Biological Activity: N-terminus containing glucosyltransferase domain; Acts on small GTPasesinvolved in cytoskeleton regulation B: Binding: 37 or 19 repeats of oligopeptides at C-terminal; Involved in receptor binding C: Cutting: Cysteine protease domain; Promotes autocatalytic cleavage of toxin D: Delivery: delivery domain; Involved in translocating toxins into cytosol

Question 31

what does the 027 ribotype produce?

Answer 31

``` produces Cdt(a binary toxin) •Also produces more TcdAand TcdB(16 and 23 fold respectively) ```

Question 32

what is c. diff toxins mechanism? A and B

Answer 32

1. Toxin binds to host receptor 2. Internalised via endocytosis 3. Endosome acidified and pore formed 4. GTD released into cytoplasm 5. Glycosylation of Rho GTPases 6. Cytotoxic and Cytopathic effects

Question 33

What is the C. diff CdT toxin mechanism?

Answer 33

1. Toxin binds to host LSR receptor 2. Internalised via endocytosis 3. Endosome acidified and pore formed by CdtBand CdtAreleased into cytoplasm 4. Cdtainhibits actin polymerization near cell membrane 5. Fibronectin microtubules elongated and project through microvilli →↑ C. diff attachment

Question 34

what is the c. diff treatment?

Answer 34

* 1stepisode of mild to moderate infection, •Oral metronidazole 400mg every 8h for10–14 days•Metronidazole Intolerance: oral vancomycin 125mg every 6h for 10 days * 2ndepisode of infection ORsevere infection ORinfection not responding to metronidazole •Oral vancomycin•Can be replaced by Fidaxomicin•Suggested duration of treatment 10–14 days * For infections which don’trespond to vancomycin or fidaxomicin•Oral vancomycin & IV metronidazole•Suggested duration of treatment 10–14 days•Can be adapted based on patient type

Question 35

what are the NICE recommendations for faecal transplantants?

Answer 35

hould only be considered for patients with recurrent C. difficileinfections that have failed to respond to antibiotics and other treatments. - encourages further reasearch