MODULE 10 Flashcards
what is minimun inhibitory concentration
is the lowest amount of antibiotic that can be used to kill or inhibit growth of bacteria
Gram negative outermebrane
outer leaflet is LPS and innerleaflet is phospholipids
- creaates an impermeable barrier requiring membrane proteins for transport
LPS composition
O-antigen is on the very outside and all LPS has same 3-5 sugar units- it is disguishing of cells and is an antigenic portion potential for vaccine target since on outside and is repeating in the cell
- change o antigen structure to evade immune response
core polyscharride is negatively charged becuse it has the phosphates and kdo sugars and is made of brached sugars contributing to bulkyness
lipid A is negativly charged becuse of phosphates on glucosamines it is what touched the phospholips of the inner leaflet
- responsible for endotoxins which can cause fever and septic shocjk
How does the LPS contribute to the barrier functions
amphipathic - hydrophobic o antigen and hydrophillic core polyscarride and lipid A
negatively charged cor polyscarride and lipid A and is sterically bulky
Whast are idvalent cations used for
divalent cations are used to stablize the membrane from the electrostac repulsion of the lipid a and the core polyscarridee wheich are both negative . Divalent cations can be mg2+ or ca2+
Outer membrane functions
- barrier for nutrients and wast and antibiotics- becuse it amphipatic and steric
- hydrophbic can cross cpm but is harder for outmembrane since it is amphpathic making gram positive more susceptible to many antibiotics
- living with degragative enzymes like lyzozomes gram pos is more prone to being degraded their disaccaride sugars but the outer membrane creates a barrier from the GI tract - steric bulk prevent enzymes from entering
- they live in enviroments with detergents (bile) which solubilize lipid bilyaer- so the cytoplasmic membrane is easlity solublized ut outermembre is resistant - even though the LPS and outermembrane is amphptic the hydrophillic o antigen keeps the detergent from reaching the hydrophobic regiomns
divalent cations uses in cross briding and disturbance
divalents cations are needed for cross briding if their a a suffiencint amount it will form crossbridges with lipid A
when their is an ineffecient amount of Mg2+ then bacteria modify lipid A to 4AA
4AA is linked to the other 4AA by electrostici atttraction
Colistin
colistin is specific to gram negative becuse it interacts with LPS lipid A and acts as a divalent cation to bind to the phosphate
- MG2+ levels can confer resisitence to colistin- when Mg2+ is high then cells are senstive to collistitn but are resistancet if they have low Mg2+
- bacteria have generated resistance by chnaging lipid A into 4AA so that colistin cant bind- done through a HGT gene called mcr-1
MCR-1 attachs a positive charge to lipid A just like 4AA has a positive charge on the end
what are proteins for import and export
Import - porins and receptors
export are secretion systems and efflux pumps
Outer membrane proteins use and consitis of
lipoproteins and b barrels
they anchor the PG to the outermembrane
What are proins and an example of them
they help import nutrients to the bacteria and are channels in the outermembrane - B-barrels
- they are watter filled and trimeric
- they are selective and can chnage to cause resistance by becoming more narrow or decreaing production (but this can also be bad for bacteria becuse they need nutrients)
LPS assembly mechanism and why it is diffucult to transport
LPS is assembled in the cytoplasmic membrane and has to cross the periplasm and outer membrane but is diffucult becuse it is amphipathic
therefore uses the lpt pathway
to transport the LPS to the outer membrane then LptD B barrel protein to translocate the LPS through the membrane
braiums lipoprotein
attaches the outer membrane and PG- covalent
Gram positive cell wall components
thick PG layer and has teichoic acids
teichoic acids composititon and types
negtively charges (has phospahte) and has linear polymers of glycerol and has d-ala
wall teichoic acids attached to NAM or peptide in PG and extended past the PG surface
lipoteichoic acid which is attached to glycolipids in the cytoplasmic membrane
Functions of teichoic acids
anchor cell wall to cytoplasmic membrane
- bind cations and controls access to cell wall surfaceregulating where PG is degraded and D-alanylation protects against antibiotics
teiohic acids in the role of infections
recognizzed by the innate immune system by MAMP which activate for pattern recognition receptors such as TLRs
mycobacteria
are gram positive bacteria that require acid fast staining becuse they have a outermembrane but made of mycolic acids not LPS
