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Microbiology ` microbiology—aNtimicrobials Microbiology ` microbiology—aNtimicrobials SEcTioN ii 191

Protein synthesis inhibitors Specifically target smaller bacterial ribosome
Aminoglycosides (30S) Initiation complex formation (70S, made of 30S and 50S subunits), leaving
50S human ribosome (80S) unaffected.
Linezolid 70S
(50S) 30S All are bacteriostatic, except aminoglycosides
M
(bactericidal) and linezolid (variable).
Initiation M
Initiator tRNA U A C
5´ A U G C A U G A U 3´ 30S inhibitors
mRNA U A C E P A
Aminoglycosides
Tetracyclines
H
M
50S inhibitors
G U A
U A C A-site tRNA binding Tetracyclines (30S) Chloramphenicol, Clindamycin
A U G C A U G A U Erythromycin (macrolides)
5´ 3´
E P A Linezolid
Peptidyl transferase Chloramphenicol
(50S)
“Buy AT 30, CCEL (sell) at 50.”
M
M H
H Elongation M
U A C
G U A U A C G U A
5´ U G A 3´ A U G C A U G A U A U G C A U G A U
5´ 3´ 5´ 3´
Termination E P A E P A
Macrolides and
Translocation
Clindamycin (50S)
Aminoglycosides Gentamicin, Neomycin, Amikacin, “Mean” (aminoglycoside) GNATS caNNOT
Tobramycin, Streptomycin. kill anaerobes.
mecHaNism Bactericidal; irreversible inhibition of initiation
complex through binding of the 30S subunit.
Can cause misreading of mRNA. Also block
translocation. Require O 2 for uptake; therefore
ineffective against anaerobes.
cliNical Use Severe gram ⊝ rod infections. Synergistic with
β-lactam antibiotics.
Neomycin for bowel surgery.
aDVerse eFFects Nephrotoxicity, Neuromuscular blockade
(absolute contraindication with myasthenia
gravis), Ototoxicity (especially with loop
diuretics), Teratogenicity.
mecHaNism oF resistaNce Bacterial transferase enzymes inactivate the
drug by acetylation, phosphorylation, or
adenylation.

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