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MECHANISMS OF ACTION OF ANTIBIOTICS
BACTERIOSTATIC AGENTS
Sulfonamides
Drugs inhibiting protein synthesis except aminoglycosides (macrolides, chloramphenicol, tetracyclines etc).
BACTERICIDAL AGENTS Beta lactams (penicillins, cephalosporins,
imipenem)
Trimethoprim/sulfamethoxazole
Vancomycin
Fluoroquinolones
Aminoglycosides
MECHANISMS OF ACTION Inhibitors of cell wall synthesis
Drugs altering cell membranes
Inhibitors of protein synthesis
Antimetabolites
Inhibitors of nucleic acid synthesis.
DRUGS INHIBITING CELL WALL SYNTHESIS Penicillins
Cephalosporins
Imipenem
Vancomycin
Fosfomycin
β-lactams
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Plus penicillin
Spheroplast
Emerging Spheroplast
Dividing Bacteria
Division
Growth site
Growth
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Mur NAc
X
Glycopeptide Polymer
X
Mur NAc
Glycopeptide Polymer
X
Glycopeptide Polymer
D-Alanine
Transpeptidase
Penicillin Binding Proteins
Transpeptidases
Carboxypeptidases
Endopeptidases
Penicillin
AUTOLYSINS
All Beta lactam antibiotics act by the same mechanism
PENICILLINS ACTIVE VS GRAM - BACTERIA
S
C
CC
C
C
N COOHO
CH3
CH3NCO
R
Penicillinase
S
C
CC
C N COOH
CH3
CH3NCO
R
OHO
Penicilloic Acid
(β-Lactamase)
COMBINATIONS WITH BETA LACTAMASE INHIBITORS
Penicillin plus a beta lactamase inhibitor.
CEPHALOSPORINS AND IMIPENEM
Same mechanism of action as penicillins but bind to different binding proteins.
FOSFOMYCIN
Inhibits peptidoglycan synthesis at an earlier stage than where the beta lactams act.
VANCOMYCIN
Enzyme
Enzyme
NAG-NAM
D-ALA
L-GLU
LYS
D-ALA
D-ALA
Transpeptidase
PENICILLINS
X
NAG-NAM
D-ALA
L-GLU
LYS
D-ALA
D-ALA
Enzyme
VAN
Transglycosylase
RESISTANCE TO BETA LACTAMS
Penicillinase Beta lactamases
S
C
CC
C
C
N COOHO
CH3
CH3NCO
R
Penicillinase
S
C
CC
C N COOH
CH3
CH3NCO
R
OHO
Penicilloic Acid
METHICILLIN RESISTANCE
Altered PBP’s.
RESISTANCE TO OTHER BETA LACTAM ANTIBIOTICS
Most prevalent mechanism is hydrolysis by beta lactamases.
Cephalosporins have variable susceptibility to βlactamases.
Some even induce formation of the enzymes.
RESISTANCE TO VANCOMYCIN
ANTIBIOTICS AFFECTING CELL MEMBRANES
Polymyxins Daptomycin
POLYMYXINS
Surface active amphipathic agents.
Interact strongly with phospholipids and disrupt the structure of cell membranes.
DAPTOMYCIN
Depolarizes the cell membrane
ANTIBIOTICS INHIBITING PROTEIN SYNTHESIS
Macrolides Clindamycin Linezolid Streptogramins Chloramphenicol Tetracyclines Aminoglycosides
50S
30S
Procaryotic Ribosome
70S--M.W.2,500,000
60S
40S
Eucaryotic Ribosome
80S--M.W. 4,200,000
Antibiotics binding to the 50S ribosomal subunit and inhibiting protein synthesis
Erythromycin and other macrolides
Chloramphenicol
Linezolid
Streptogramins
Antibiotics binding to the 30S ribosomal subunit and inhibiting protein synthesis
Aminoglycosides
Tetracyclines
CLEanS AT
Macrolides (Erythromycin, Azithromycin and Clarithromycin)
aa
A50S
30S
mRNA
template
Transferase site
P
Nascent polypeptide chain
MACROLIDES
TRANSLOCATION
CHLORAMPHENICOL
aa
A50S
30S
mRNA
template
Transferase site
P
Nascent polypeptide chain
Chloramphenicol
Mechanism of action of Chloramphenicol
INITIATION
STREPTOGRAMINS
Quinupristin/Dalfopristin (30:70)
aa
A50S
30S
mRNA
template
Transferase site
P
Nascent polypeptide chain
QUINUPRISTIN(MACROLIDE)
DALFOPRISTIN
INITIATION
AMINOGLYCOSIDES
Bind irreversibly to the 30S subunit.
Exact mechanism of cell death is unknown.
Postantibiotic effect.
A50S
30S
mRNA
template
Transferase site
P
Nascent polypeptide chain
Tetracycline
aa
INHIBITION OF MITOCHONDRIAL PROTEIN SYNTHESIS
Mitochondrial ribosome resembles bacterial ribosome.
May account for some toxic effects (e.g. chloramphenicol, linezolid).
RESISTANCE
Alterations in ribosomal proteins (e.g. macrolides).
Decreased permeability to the antibiotic.
TetracyclineATP
TETRACYCLINE RESISTANCE
ANTIBIOTICS ACTING AS ANTIMETABOLITES
Sulfonamides
Trimethoprim plus sulfamethoxazole
2HN COOH
DIHYDROPTERIDINE
PYROPHOSPHATE DERIVATIVE
DIHYDROPTEROIC ACID
DIHYDROFOLIC ACID
FOLIC ACID BIOSYNTHESIS
Glutamic Acid
2 ATP
2HN SO2NH2
Dihydropteroate
Synthetase
TRIMETHOPRIM-SULFAMETHOXAZOLE
2HN CH2
OCH3
OCH3
OCH3
80 mg TRIMETHOPRIM
O
2HN SO2NH
N CH3
400 mg SULFAMETHOXAZOLE
PABA
DIHYDROPTEROIC ACID
DIHYROFOLIC ACID
TETRAHYDROFOLIC ACID
+ Pteridine
SULFONAMIDE
TRIMETHOPRIMDihydrofolate Reductase
Dihydrofolate Synthetase
Dihydropteroate Synthetase
Advantages of sulfonamide-trimethoprim combination
Results from multiple mechanisms.
Altered dihydropteroate synthetase.
Cross-resistance among all sulfonamides.
SULFONAMIDE-RESISTANCE
ANTIBIOTICS AFFECTING NUCLEIC ACID SYNTHESIS.
Fluoroquinolones
Metronidazole
Rifampin
FLUOROQUINOLONES
FLUOROQUINOLONES
Gyrase (Topoisomerase I)-older quinolones
Topoisomerase IV-3rd and 4th gen quinolones.
FQ RESISTANCE
Changes in gyrase and topoisomerase
Increased efflux
Inactive End ProductsInactive End Products
MetronidazoleMetronidazole
MetronidazoleMetronidazole
Short lived Short lived intermediatesintermediates
Inactive endInactive end productsproducts
DNADNARNARNA
ProteinProteinOther targetsOther targets
Mechanism of Mechanism of action of action of metronidazole on metronidazole on an anaerobic an anaerobic organismorganism
Ferredoxin Ferredoxin reducedreduced
RIFAMPIN
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