Presentations Flashcards
What are efflux systems?
Efflux pumps transport substrates from the cytoplasm across PM, in Gram -ve also across outer membrane, and extrude toxins, quorum sensors, biofilm, and virulence factors of the bacteria - as well as efflux of antibiotics.
Primary efflux pumps - translocation driven by energy from ATP hydrolysis.
Secondary - draw energy from electrochemical gradients by PMF/ion pumps.
What are the different class of efflux pumps?
Primary efflux pumps - translocation driven by energy from ATP hydrolysis.
Secondary - draw energy from electrochemical gradients by PMF/ion pumps.
What is substrate redudnancy?
A single antibiotic can be exported by different efflux pumps.
1 efflux pump can export diverse substrates…
= PROBLEM if designing inhibitors, as will need to be broad-spectrum inhibitors to inhibit ALL the efflux systems.
What are the efflux pumps of Gram +ve and Gram -ve bacteria?
Gram -ve:
RND superfamily:
ABC superfamily (-ve)
RND pump Acr-AB-TolC in E.coli
Gram +ve:
MFS, MATE, PACE, SMR, ABC superfamily (+ve):
Pump NorA - 12TM segments, in Staphylococcus Aureus (MFS superfamily)
How can active efflux pumps be overexpressed?
Major contributor to ABR:
Develop multi-drug resistance.
Stress responses triggered by high conc. exposure to antibiotics.
MATE family = 2ndary efflux pump = Fluroquinolones effluxed.
What causes Anthrax?
Bacillus Anthracis - an endospore forming, Gram +ve, rod bacteria.
In elevated CO2, 37 degrees, will produce it exotoxin…
EXOTOXIN composed of 3 parts.
plasmid genes activated:
pXO1 = anthrax toxins.
pXO2 - anitphagocytic capsule.
What is the structure of anthrax toxin?
An exotoxin - encoded by pXO1 plasmid genes.
Protective antigen (PA), Edema factor (EF) and lethal factor (LF).
LF and EF form a complex with PA, forming the Edema toxin or Lethal toxin.
Endocytosis and endosomal uptake, escape and cytosolic actiivity.
What are the effects of the anthrax toxins?
Lethal toxin = protease cleaving MAPK1 and MAPK2, inhibiting MAPK pathways.
= Necrosis.
EF - reduces CA2+/Calmodulin dependent AC activity.
= Edema
What type of toxin is Anthrax’s?
Anthrax toxins are exotoxins - proteins encoded by plasmid pXO1 genes, forming Lethal and Edema factors, which form a complex with Protective antigen (PA) - to form Lethal toxin and Edema Toxin.
Therefore, Type III exotins = A-B toxins.
A= active enzymatic component and modifies intracellular 2nd messenger.
B = PA, B component determines cell specificty (PA), phagocytic cells, endothelial cells etc,
What are endo and exotoins?
Exotoxins are secrreted, but endotoxins are released upon microbe death.
Exotoxins are peptides, tend to be secreted by Gram +ve.
= Can be superantigens and trigger dysregulated host immune responses, and widespread T-cell activation and cytokine storms.
Endotoxins are lipopolysacchardies (LPS), - O antigen, core oligosacchardide, and hydrophobic Lipid A anchor.
What antibiotics target the cytoplasmic stage of cell wall synthesis?
Fofomycin and Cycloserine:
Fosfomycin inhibits MurA enzyme - which converts UDP-NAG into UDP-NAM.
Cycloserine - prevents formation of NAM-pentapeptide (by blocking D-Ala-D-ala dipeptide addition).
What antibiotics target the membrane-associated stage of cell wall synthesis?
Bacitracin - inhibits transport of peptidoglycan precursors by preventing dephosrylation of Bactoprenol (so cannot cross PM).
Vancomycin - Binds to D-ala-D-ala dipeptide at end of UDP-NAM-pentapeptide. = prevents transglycosylation and transpeptidation steps required for cell wall synthesisl.
What are beta lactamases?
Enzymatic degradation of antibiotics.
Hydrolyse beta lactam ring of beta lactam antibiotics (Penicillins, cephalogpsorins etc)
How are beta lactamses encoded?
Genes responsible for enzymes are localised on mobile genetic elements - plasmids, transposons etc.
BLA genes in Gram -ve bacterie like E.Coli.
Rapidly transferred.
What are ESBLs?
extended spectrum beta lactamases:
BLA-NDM-1 gene in plasmids of Gram -ve bacteria.
E.Coli and Klebsiella Pneumoniae:
= only carbapenems are effective agents.
