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40 Cards in this Set

  • Front
  • Back
What are the two bases for selective toxicity
Structural differences in the target and permeability differences
What are the three main steps of protein synthesis in bacteria
Amino acid activation, Formation of 30S and 70S initiation complexes, and polypeptide chain synthesis
What does amino acid activation involve
Formation of charged tRNA
What are the translational events of protein synthesis
Recognition, peptidyl transfer, translocation, release
What drugs inhibit amino acid activation
There are none
What drugs inhibit formation of initiation complexes
Linezolid (Zyvox) is the only drug that inhibits formation of the 70S complex. In a class of antibiotics called oxazolidinones. It prevents the formation of the N-formylmethionyl-tRNA-mRNA-70S ribosomal ternary complex by binding to the 23S peptidyltransferase center of the 50S ribosomal subunit. It is bacteriostatic
What drugs inhibit recognition
Streptomycin and related aminoglycosides (kanmycin, tobramycin, gentamycin, neomycin, amikacin, paramomycin)
What type of drugs are the aminoglycosides
Broad spectrum, bactericidal antibiotics for both gram positive and negative. They target specific proteins in the 30S ribosomal subunit
What is the mechanism of action of streptomycin
At low concentrations, or in the case of ribosomes engaged in polypeptide elongation, streptomycin primarily causes misreading. Due to distortions of codons in the recognition region of the A-site
What are streptomycin-dependent mutants
Bacteria that require streptomycin binding to restore a mutationally altered recognition region to the proper conformation
How does streptomycin kill bacteria
Killing action is due to cyclic polysomal blockade. The drug does not prevent formation of a 70S initiation complex; however, once the complex is formed it is unstable and rapidly dissociates
What is required for streptomycin to inhibit protein synthesis
Some faulty protein synthesis due to misreading, facilitating drug entry into the cell
What does streptomycin bind to
The S12 protein of the 30S ribosomal subunit (Wikipedia says its the 23S rRNA bacterial ribosome)
Why don't aminoglycosides harm the host
Absence of their specific protein targets in host cell 40S ribosomal subunits. Also, they are not actively transported into euckaryotic cells
How do the aminoglycosides differ from one another aside from their respective structures
All have the same general mechanism of action, but they do not have common binding sites on the 30S ribosomal subunit. They also differ with respect to their spectra, their ability to enter bacterial cells, and their susceptibility to inactivation
How can resistance to aminoglycosides develop
Mutation of the target protein in the 30S ribosomal subunit; decreased uptake of the antibiotic; enzymatic modification of the antibiotic
What do newer aminoglycosides bind to
Both the 30S and the 50S ribosomal subunit
What are the negative aspects of aminoglycoside therapy
Resistance emerges with high frequency; Ototoxicity and nephrotoxicity; Action antagonized by anaerobiasis, acid pH, and polyvalent ions; ineffective against intracellularly localized bacteria
What are the positive aspects of aminoglycoside therapy
Rapid bactericidal effect in sensitive cells; Broad spectrum; slow development of resistance in newer drugs
What are the characteristics of spectinomycin
Not a true aminoglycoside. Bacteriostatic. Causes formation of unstable 70S, but does not cause misreading and does not inhibit polysomal ribosomes. Used against Beta-lactamase producing gonococci or to treat gonorrhea in patients allergic to penicillin
What are the characteristics of the tetracyclines
Broad spectrum, bacteriostatic. Effective against Chlamydia, Mycoplasma, Rickettsia, and other gram positive and negative bacteria. They bind to the 30S ribosomal subunit and inhibit binding of aminoacyl-tRNA to the A-site. Selective toxicity due to energy-dependent uptake of the drugs by bacteria. Useful against intracellular bacteria
What are the inhibitors of peptidyl transfer
Chloramphenicol, Lincomycin, and Clindamycin
What type of drug is chloramphenicol
Broad spectrum, bacteriostatic.
What is the mechanism of action of chloramphenicol
Binds reversibly to the 50S subunit and alters the tRNA at the P site
What is the selective toxicity of chloramphenicol due to
Inability to enter mitochondria.
How is resistance to chloramphenicol achieved
Plasmid encoded acetyltransferases catalyze the acetylation of the 3-hydroxy group, making it incapable of binding 50S. There can also be mutations in outer membrane porins
What type of drugs are lincomycin and clindamycin
Bacteriostatic, narrow spectrum
What are lincomycin and clindamycin used for
Effective in the treatment of infections caused by gram positive bacteria. Clindamycin is effective against staphylococci and anaerobic gram negative bacteria
How is resistance to clindamycin achieved
Methylation of 23S ribosomal RNA. This also results in resistance to erythromycin
What antibiotics inhibit translocation
Erythromycin, Azithromycin, clarithromycin, Telithromycin
What are three macrolide antibiotics
Erythromycin, azithromycin, clarithromycin
What are the characteristics of macrolide drugs
Macrocyclic lactone chemical structure. Bacteriostatic and bind with ribosomes from bacteria to prevent the production of proteins
What is the mechanism of action of the macrolides
Binding to 50S, which prevents peptidyl tRNA from returning to the P site from the A site. This prevents ejection of free deacylated tRNA from the P site
How is resistance to the macrolides achieved
Methylation of the 23S RNA of the 50S ribosome. Can also be due to hydrolysis of the lactone ring or active efflux of the drug
What are the ketolide antibiotics (Telithromycin)
New family of drugs. Bind with the exit tunnel of the large ribosomal subunit, thus blocking the exit of nascent polypeptides
Why are the aminoglycosides ineffectual in the treatment of infections involving abscess formation
They are not actively transported into eucaryotic host cells, so they can never reach the bacteria
What would happen to the viability of a chloramphenicol-sensitive organism if it were washed free of the drug
Growth would resume, since Chloramphenical reversibly binds 50S, upsetting peptidyl transfer
Which of the antibiotics that inhibit protein synthesis have the 50S ribosomal subunit as their target
Chloramphenicol; Erythromycin and the macrolides; possibly Telithromycin and the ketolides
Which antibiotic inhibits formation of the initiation complex
Linexolid (Zyvox), an oxaxolidinone
Why are antibiotics that inhibit either peptidyl transfer or translocation also inhibitors of the puromycin reaction
Puromycin inhibits translation by causing premature termination. It does this by binding to the A site in place of tyrosyl-tRNA during transpeptidation. The listed antibiotics also cause premature termination