J Letchford Lec 1 Modes of action Flashcards
Antimicrobials are chemicals which kill or ____ microbial growth.
Inhibit
Bacteriostatic =
Bactericidal =
Inhibit
Kill
Most antimicrobials only kill actively _____ bacteria so also rely on host immune system to eradicate all bacteria.
Growing
What are the 4 main sites of anti-microbial action?
1) Cell Wall
2) Cell membrane (x many targets as pro & eukaryote cell mem are similar)
3) Nucleic acid synthesis
4) Protein synthesis (side effects as pro & eukaryote ribosomes are similar)
What makes up the bacterial cell wall?
How are the neighbouring molecules in this held together?
- Peptidoglycan (large macromolecule)
- Glycosidic bonds hold residues together and 3rd AA and terminal AA of glycan chains cross-link by short peptide bridges.
The glycol chains act as a backbone to ______, and is composed of altering residues of N-___ ____ ____ (NAM) and N-____ _____ (NAG).
Peptidoglycan
N-Acetyl Muramic Acid
N-Acetly Glucosamine
In peptidoglycan cell walls, each molecule of NAM has a pentapeptide attached consisting of AAs. This glycan pentapeptide repeat unit is ____-_____ to adjacent ____ chains, through direct _____ linkage or ____ inter-bridge.
Cross-Linked
Glycan
Peptide
Peptide
For PG cross linking to occur, _______ are needed.
Transpeptidases
How do B-lactams exert their action?
1) They bind Penicillin Binding Proteins (PBPs)
- Transpeptidases (needed to cause cross linking)
This then prevents cross-linking between neighbour peptide side chains.
Cells then lose shape due to lack of proper cell wall and the cell dies.
2) Mimic d-ala-d-ala residues on peptide side chain to prevent cross linking
3) Stimulate autolysins - break down cell wall (indirect effect)
- Gram negative bacteria have an ____ ______ that is not present in Gram positive bacteria.
- Gram negative bacteria have thinner/thicker peptidoglycan layer than gram positive bacteria
- B lactam drugs need to get through the outer membrane and peptidoglycan layer before binding to _____ ____ _____ on the cytoplasmic membrane and inhibiting cross linking.
Outer membrane
Thinner
Penicillin binding protein
Glycopeptides inhibit the synthesis of the ___ ___.
Two examples of glycopeptides are _____, ______.
These antimicrobials bind terminal _-__ - _-__ on peptide side chain, preventing _________ enzyme from adding PG monomer onto glycan chain.
It prevents cross linking
Cell wall
Vancomycin and Teicoplanin
d-ala - d-ala
Transglycosylase enzyme
Polymyxins are inhibitors that act at the ___ _______.
e.g Polymyxin B and E (Colistin)
These drugs work on gram _ve bacteria.
Why is this?
Cell membrane
Negative
Because Polymyxins act on the cell membrane and gram positive bacteria do not possess an outer membrane.
Polymyxins disrupt the cells outer _____ causing _____ of cytoplasmic contents.
Membrane
Leakage
Some antimicrobials act on ______ Acid (NA)
Metabolic inhibitors of NA synthesis
e.g S_______des & T______im
Nucleic Acid
Sulfonamides and Trimethoprim
Some antimicrobials affect ____ replication
e.g F_______ones
DNA
Fluoroquinolones
Some antimicrobials affect ___ polymerase
e.g ____mycins
RNA
Rifamycins
Some antimicrobials affect DNA directly
e.g Nitro_____oles and Metra_____
Nitroimidazoles
Metranidazole
Inhibitors of ____ replication include
C______acin (gram-) and L______acin (gram+&-)
These antimicrobials either Type 2 (DNA ____) AND/OR Type 4 ________.
DNA
Ciprofloxacin and Levofloxacin
Gyrase
Topoisomerase
DNA Gyrase: removes DNA _____ ahead of replication fork
Supercoils
Topoisomerase 4: separates out DNA after _____.
Replication
Inhibitors of Protein synthesis: M\_\_\_\_\_des Strep\_\_\_\_mins Linc\_\_\_\_des Oxaz\_\_\_\_\_\_ones Amin\_\_\_\_\_\_ Tet\_\_\_\_\_\_ Chlor\_\_\_\_\_\_\_ Fusi\_\_ \_\_\_\_
Macrolides Streptogramins Lincosamides Oxazolidinones Aminoglycosides Tetracyclines Chloramphenicol Fusidic acid
__s ribosomes and __s ribosomes come together to make __s ribosomes
30s and 50s to make 70s
Protein synthesis:
INITIATION:
1) fmet-tRNA brought to ___ start codon (_ site)
2) 30s subunit attaches to ____
3) __ subunit completes initiation complex
ELONGATION: 1) 2nd \_\_\_\_ enters A site 2) Peptide bond between 1st and 2nd \_\_. 3) Translocation and release of \_\_\_. 1st \_\_\_\_ comes off ribosome 2nd \_\_\_\_ enters P site 3rd \_\_\_\_ enters A site
TERMINATION (reach stop codon)
AUG (p site)
mRNA
50s
tRNA AA tRNA tRNA tRNA tRNA
Inhibitors of protein synthesis:
Aminoglycosides/Oxazolidinones (Cidal agents)
e.g G_____ / L_____
MOST AG’s bind __ subunit:
DECREASE initiation and assemble of _____
DECREASE binding of ____ in _ site and translocation
SOME AG’s and Oxazolidinones bind ___ subunit:
DECREASE assemble of _______ complex.
Gentamicin
Linezolid
30s
Ribosome
tRNA in A site (acceptor site)
50s
Initiation
Inhibitors of protein synthesis:
Tetracyclines (Static agents)
e.g D_______, M______
Bind ___ subunit of ribosome
DECREASE binding of _____ in _ site
Doxycycline
Minocycline
30s
tRNA in A site (acceptor site)
Inhibitors of protein synthesis:
Chloramphenicol
Binds to __ subunit
DECREASES peptide ____ formation
50s
Bond
Inhibitors of protein synthesis:
Macrolides
e.g E______, C______
Binds __ subunit
DECREASES ______ and release of tRNA
(doesn’t affect peptide bond formation but the ribosome can’t move along the strand! - this means incomplete polypeptides are released)
Erythromycin
Clarithromycin
50s Translocation (ribosome moving along mRNA)
Inhibitors of protein synthesis
Fusidic acid
Binds to EF-_ ribosome complex
DECREASES translocation of tRNA from _ to _ site
EF-G (elongation factor that supplies energy for translocation)
A site to P site
Other antimicrobials:
Affecting cell wall synthesis:
Cycloserine, Bacitracin
Acting on cell membrane
Dapto___ (Cubicin)
Affecting protein synthesis
Lincos___, Streptogramins
Affecting nucleic acid
Sulfon____/ Tri_____, Rifa____
Daptomycin
Lincosamides
Sulfonamides, Trimethoprim, Rifamycins
