micro 6 Flashcards
what is shiga toxin producing e.coli also known as?
•Verocytotoxin producing E. coli
what is a subset of shiga toxin producing e.coli?
- A subset of these can be called EnterohemorrhagicE. coli (EHEC)
- All EHEC are STEC but not all STEC are EHEC
how infectious is STEC?
- STEC infectious dose is low
* Believed to be <100 cells (some say <10)
what are the two main variants of STEC?
2 main variants Stx1 andStx2
are the STEC variants the same?
•Antigenically different but same mechanism of action
what are the STEC variants used for?
Used as markers for identification (PCR/multiplex PCR
what is STEC associated with?
Associated with hemorrhagic colitis and hemolytic-uremic syndrome.
what was the first iscolated STEC?
E.coli 0157:H7
how can E.coli 0157:H7 be spread?
- Major foodborne pathogen
* Can be spread person-person through faecal shedding
what are STEC 0157 ?
refers to EC strains which are 0157 but not necessarily H7 variants
what are shiga toxins and where are they most commonly found?
- Family of toxins that are most commonly found in Shigella dysenteriae and some STEC serotypes
- Extremely potent bacterial toxin
what are the two units which shiga toxins are composed of?
- Comprised of 2 units
* A (1 copy)•B (5 identical copies)
how does shiga toxin producing e.coli work?
- Bacteria binds to cell surface a)Intimin protein
- B subunit binds to glycolipic globotriaosylceamide (Gb3)
- Internalised within an endosome
- Transported to Golgi a)A1 subunit is cleaved from B pentamer
- Inhibits protein synthesis
- Cell death
what was clostridioides difficile known as?
•Was originally Clostridium difficile•Technically renamed in 2016
what is c. difficle known for?
One of the most important healthcare associated MDR pathogens- NOT TRAVLERS DIAHORREA
does c. difficile form spores?
- It forms SPORES and is ANAEROBIC!!•Lets it resist disinfection
- Cant survive in oxygen
what is a way of subdividing strains based on the 16S-23S intergenic spacer region?
C. diff ribotypes
what strain of the c. difficle causes the most severe disease?
•027 ribotype causes more severe disease
what are c. diff toxinotypes?
are a group of strains that have changes in the toxin A and B coding region
•Known as PaLoc(Pathogenicity locus)
how are c. diff ribotypes and toxinotypes done?
•Done by looking at PCR restriction fragment length polymorphism
which toxinotypes have small and large variations?
- Toxinotype III has small variations
* Toxinotype X and XVII have large deletions in tcdA
are c. diff spores metabolically dormant?
yes-•Can resist disinfection and environmental stress
what are the differnt layers of a C.diff spore?
•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
what effect do antibiotics have on c. diff?
- Use of broad spectrum antibiotics can disrupt normal microflora
- Removes competition allowing C. diff to grow