Cell Membrane Labilizer Part 2

Polymyxins - Mechanism of Action

Disrupt bacterial cell membrane integrity by interacting with membrane phospholipids.

Primary target of polymyxins

Cell membrane phospholipids of Gram-negative bacteria.

Polymyxins act similarly to

Cationic detergents.

First step in polymyxin action

Binding to lipopolysaccharides (LPS) and phospholipids of the outer membrane.

Binding of polymyxins to bacterial membranes

Electrostatic interaction.

Why polymyxins bind strongly to Gram-negative bacteria

Their outer membrane contains negatively charged lipopolysaccharides.

Polymyxins are

Cationic molecules.

Bacterial endotoxins are

Anionic molecules.

Major membrane component displaced by polymyxins

Calcium and magnesium ions.

Role of calcium and magnesium ions in bacteria

Stabilize the outer membrane.

Effect of polymyxin displacement of calcium and magnesium

Loss of membrane stability.

Result of membrane destabilization

Increased membrane permeability.

Effect of increased membrane permeability

Leakage of intracellular contents.

Intracellular materials lost after polymyxin exposure

Amino acids, nucleotides, potassium, and other cellular constituents.

Final result of polymyxin membrane damage

Bacterial cell death.

Why polymyxins are bactericidal

They cause irreversible membrane damage.

Polymyxins affect which membrane function?

Selective permeability.

Polymyxins affect which membrane property?

Osmotic regulation.

Polymyxins affect which membrane process?

Transport of essential molecules.

Detergent-like action of polymyxins

Disrupts membrane structure and function.

Cell death from polymyxins occurs due to

Loss of membrane integrity.

Polymyxins act rapidly because

The cell membrane is an essential structure.

Polymyxins do not require

Rapid bacterial multiplication.

Why polymyxins can be combined with bacteriostatic drugs

Their activity is independent of bacterial growth rate.

Additional mechanism of polymyxins

Binding and neutralization of endotoxins.

Polymyxins bind to which endotoxin component?

Lipid A portion of lipopolysaccharide.

Effect of endotoxin binding

Reduction of endotoxin activity.

Clinical significance of endotoxin binding

May help in endotoxemia.

Additional pharmacologic effect of polymyxins

Antipyretic activity.

Main bacterial structure targeted by polymyxins

Cell membrane.

Main bacterial structure targeted by beta-lactams

Cell wall.

Difference between polymyxins and beta-lactams

Polymyxins damage membranes while beta-lactams inhibit cell wall synthesis.

Difference between polymyxins and aminoglycosides

Polymyxins target membranes while aminoglycosides target ribosomes.

Difference between polymyxins and tetracyclines

Polymyxins target membranes while tetracyclines inhibit protein synthesis.

Difference between polymyxins and sulfonamides

Polymyxins disrupt membranes while sulfonamides inhibit folate synthesis.

Why Gram-positive bacteria are less susceptible to polymyxins

They lack the outer membrane rich in lipopolysaccharides.

Why Gram-negative bacteria are susceptible to polymyxins

The drug binds strongly to their outer membrane.

Most important structure required for polymyxin activity

Lipopolysaccharide-containing outer membrane.

Polymyxins primarily attack which bacterial envelope layer?

Outer membrane.

Secondary membrane affected by polymyxins

Cytoplasmic membrane.

Ultimate consequence of polymyxin exposure

Cell lysis and death.

Mechanism category of polymyxins

Cell membrane labilizers.

Only major antimicrobial class in this module

Polymyxins.

Polymyxin B MOA

Disrupts bacterial cell membranes through detergent-like action.

Colistin MOA

Disrupts bacterial cell membranes through detergent-like action.

High-yield MOA association

Polymyxins = Cell membrane disruption.

High-yield MOA association

Polymyxins = Detergent-like action.

High-yield MOA association

Polymyxins = Increased membrane permeability.

High-yield MOA association

Polymyxins = Leakage of cellular contents.

High-yield MOA association

Polymyxins = Endotoxin neutralization.

High-yield MOA association

Polymyxins = Lipid A binding.

High-yield MOA association

Polymyxins = Gram-negative outer membrane target.

Most important MOA fact about polymyxins

They act as cationic detergents that destroy bacterial cell membranes.

Mnemonic for polymyxin MOA

P = Punctures membranes.

Mnemonic for endotoxin activity

P = Polymyxins Prevent endotoxin effects.

Most frequently tested MOA

Polymyxins disrupt bacterial cell membranes.

Most frequently tested comparison

Polymyxins target membranes; beta-lactams target cell walls.

Most frequently tested endotoxin fact

Polymyxins bind Lipid A and neutralize endotoxin.