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Mechanisms of Antibiotic resistance
Block 7. General mechanisms of antibiotic resistance
8
Microbiology
Graduate
08/15/2010

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Term
Efflux Pumps
Definition
Efflux pumps remove the drug from the bacteria.

They can be non-specific or specific.

They can be intrinsic, acquired, or mutational (derepression of pump expression).
Term
B-Lactamases
Definition
Gram-negative and Gram-positive bacteria produce -lactamases that will inactive penicillin by cleaving the -lactam ring.
Term
fosfomycinases
Definition
Fosfomycin is cleaved by fosfomycinases
Term
Modification of aminoglycosides/chloramphenicol
Definition
Aminoglycosides are inactivated by modification by the bacteria. There are 3 basic modifications that will inactivate Aminoglycosides:
1. N-acetylation
2. O-phosphorylation
3. O-adenylation

Chloramphenicol can be inactivated by acetylation (acetyl transferase)
Term
Target site modifications - PBP
Definition
Target site modifications will prevent antibiotic action. These include mutation to specific targets that are either acquired or mutational.

MRSA (methicillin resistant S. aureus)
mecA gene encodes a new beta-lactam resistance PBP (PBP2a)

S. pnuemoniae
PBP2X – low level resistance
PBP2B – low and high level resistance
Term
Target site modification - Methylation of 23s rRNA
Definition
MLS (macrolide-lincosamide-streptogramin) strains have a erthromycin methyltransferase gene that methylates 23S rRNA prevent interaction of macrolides and lincosamides/clindamycin with the 23S rRNA and the 50S ribosomal subunit
Term
Target site modification - Vancomycin resistance
Definition
Vancomycin resistance is acquired and encoded by 7 genes. These genes change the D-Ala-D-Ala pentapeptide to D-Ala-D-Ser or D-Ala-D-Lac. There are 3 types of Vancomycin resistance operons: VanA, VanB, VanC.
Term
Metabolic bypass
Definition
There are either modification or complete substitution of Dihydropteroic acid synthetase and Dihydrofolate reductase
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