Antimicrobial MOA

Question 1

Define antimicrobial

Answer 1

Any chemicals which kill or inhibit microbial growth in or on a body surface (fungal, viral and bacteria)

Question 2

Define antibacterial

Answer 2

Any chemical, which specifically targets bacteria and kills or inhibits its growth
Most antibacterial ONLY kill actively growing bacteria

Question 3

Define antibiotic

Answer 3

An antibacterial agent which is synthesised by microorganisms and selectively inhibit or kills off another microorganism

Question 4

Define bacteriostatic

Answer 4

slows down or stall bacteria growth

Question 5

Define bactericidal

Answer 5

Kills bacteria

Question 6

Define selective toxicity

Answer 6

Selectively kills or inhibits the target organisms, whilst causing no or minimal harm to the host

Question 7

Name the 3 ideal antimicrobial properties

Answer 7

SPECIFIC - ability of a drug/chemical agent t interact with a defined target
SELECTIVE - selectively kills or inhibits the target organism whilst causing no harm to the host
BACTERICIDAL - minimal emergence of resistance to the drug

Question 8

Name the 4 main areas of the cell that antibiotics target

Answer 8

Cell wall
cell membrane
nucleic acid
protein synthesis

Question 9

Define gram negative bacteria

Answer 9

Thin peptidoglycan layer
Outer membrane - contains lipopolysaccharide and porin channels

Question 10

Define gram positive bacteria

Answer 10

Thick peptidoglycan layer
contains teichoic acid and lipoteichoic acid
NO OUTER MEMBRANE

Question 11

Name examples that inhibit cell wall synthesis

Answer 11

Beta lactams, glycopeptides

Question 12

Name examples of antibiotics which act on the cell membrane

Answer 12

polymyxins and lipopeptides

Question 13

Name examples of antibiotics which inhibit the enzymes for DNA replication

Answer 13

fluoroquinolone

Question 14

Name the antibiotics which inhibit protein synthesis

Answer 14

tetracyclines and aminolglycosides

Question 15

Describe the MOA of beta-lactams

Answer 15

1) Bind and inhibit action of transpeptidases usually known as penicillin binding proteins (PBPs)
2) Get incorporated into peptide side chain
3) stimulate autolysis - break down the cell wall - cell lysis

Question 16

Describe the MOA of glycopeptides

Answer 16

1) Binds to terminal amino acids on the peptide side chain of the monomer
2) Prevents cross-linking of peptide side chains
3) Prevents glycolyse enzymes from adding PG monomer onto PG chain

Question 17

Why do glycopeptides only act on gram positive bacteria?

Answer 17

They cannot penetrate the cell wall, they are too big

Question 18

Describe the MOA for polymyxins

Answer 18

1) binds to lipid A
2) distorts the membrane
3) penetrates the cell wall
4) disrupts membrane integrity
5) allows leakage of cytoplasmic contents

Question 19

What is polymyxins used to treat?

Answer 19

Severe gram negative infections

Question 20

Describe the MOA of fluroquinolones

Answer 20

1) bind to and inhibit DNA gyrase and/or topoisomerase IV when complexed with bacterial DNA
2) inhibits DNA replication and packaging of DNA within the bacterial cell -> bacterial cell lysis

Question 21

Describe the MOA of tetracyclines (doxycycline)

Answer 21

1) binds irreversibly to the A-site on the 16S rRNA in 30S subunit
2) inhibits binding of the tRNA to A-site, inhibits protein synthesis
3) selectively through between binding to bacterial ribosome - better accumulation of antibiotic inside of bacterial cell

Question 22

Describe the MOA of aminoglycosides (gentamicin)

Answer 22

1) Binds irreversibly to the A-site on the 16s rRNA in 30S subunit
2) Inhibit binding of tRNA to A -site
3) Prevent formation of initiation complex
4) Cause misreading of the codons along the mRNA
5) Increase membrane permeability - more gentamicin can accumulate

Question 23

Describe the 3 phases of translation

Answer 23

Initiation - ribosome assembles around the template mRNA. the first tRNA is attached to the START codon
Elongation - tRNA transfers amino acid to the mRNA corresponding to the next codon. Ribosome the moves to the next mRNA codon to continue the process - creates an amino acid chain
Termination - when a STOP codon is reached, the ribosome release the peptide