24 Questions
What is one of the mechanisms of aminoglycoside resistance that involves modification of the drug?
Bacterial enzymes such as acetyltransferases
What is the purpose of Neomycin* when given orally?
For bowel decontamination
Which of the following mechanisms of aminoglycoside resistance does not involve modification of the bacterium?
Presence of efflux pumps
What is the general term for the enzymes that modify aminoglycosides and prevent them from binding to ribosomes?
Acetyltransferases
What is the result of decreased accumulation within the bacterium?
Aminoglycoside resistance due to the presence of efflux pumps
What is the mechanism of aminoglycoside resistance that involves a change in the bacterial ribosome?
Mutation of the bacterial ribosome
What is the name of the aminoglycoside shown in Figure 6-2?
Amikacin
Which of the following is NOT a mechanism of aminoglycoside resistance?
Inhibition of bacterial protein synthesis
What is the main mechanism of action of macrolides?
Blocking the exit of the newly synthesized peptide from the 50S ribosome
How do macrolides function in a manner similar to aminoglycosides?
By targeting the bacterial ribosome and preventing protein production
What is the location of the macrolide binding site on the bacterial ribosome?
The 50S subunit
What is the result of methylation of the ribosome binding site in some bacteria?
Impaired accumulation of macrolides within the bacterium
What is the effect of the mef gene on macrolide accumulation in some gram-positive bacteria?
It decreases macrolide accumulation
What is a common mechanism of resistance to macrolides in some bacteria?
Inhibition of drug entry and accumulation
What is the result of resistance to one member of the macrolide group?
Resistance to all members of the macrolide group
What is the structural feature of macrolides that gives them their name?
A large cyclic core called a macrocyclic lactone ring
What is the mechanism of action of efflux pumps in bacterial resistance to aminoglycosides?
Prevention of accumulation of the aminoglycoside in the cytosol of the bacterium
Which of the following is a mechanism of bacterial resistance to aminoglycosides that involves changes to the ribosome?
Mutations within the ribosome
What is the target of aminoglycoside binding in bacterial cells?
Ribosome
Which of the following is NOT a mechanism of bacterial resistance to aminoglycosides?
Inhibition of protein synthesis
What is the result of modification of the aminoglycoside in bacterial resistance?
Reduced binding of the aminoglycoside to the ribosome
Which mechanism of bacterial resistance to aminoglycosides involves the pumping of the antibiotic out of the cell?
Efflux pumps
What is the site of action of aminoglycosides in bacterial cells?
30S subunit
Which of the following is a mechanism of bacterial resistance to aminoglycosides that does not involve changes to the antibiotic?
Mutations within the ribosome
Study Notes
Macrolides
- Macrolides consist of a large cyclic core called a macrocyclic lactone ring, decorated with sugar residues.
- Macrolides bind tightly to the 50S subunit of the bacterial ribosome, blocking the exit of the newly synthesized peptide.
- They function similarly to aminoglycosides, targeting ribosomes and preventing protein production.
Mechanisms of Resistance
- Resistance to macrolides occurs by three mechanisms:
- Inhibition of drug entry and accumulation due to difficulty penetrating the outer membrane of aerobic gram-negative bacilli and active efflux pumps in some resistant bacteria.
- Enzyme-mediated ribosome binding site alteration, such as methylation, which prevents macrolide interaction.
- Mutation of the ribosome binding site, which rarely occurs.
Aminoglycosides
- Aminoglycosides are active against various bacteria, including gram-positive and gram-negative bacteria, as well as mycobacteria.
- Resistance to aminoglycosides occurs via three mechanisms:
- Efflux pumps prevent accumulation of the aminoglycoside in the cytosol of the bacterium.
- Modification of the aminoglycoside prevents binding to the ribosome.
- Mutations within the ribosome prevent aminoglycoside binding.
Antimicrobial Activity of Aminoglycosides
- Aminoglycosides are effective against:
- Gram-positive bacteria, including Staphylococci, Streptococci, Enterococci, and Listeria monocytogenes.
- Gram-negative bacteria, including Haemophilus influenzae, Enterobacteriaceae, and Pseudomonas aeruginosa.
- Mycobacteria, including Mycobacterium tuberculosis and Mycobacterium avium complex.
Learn about the structure and function of macrolides, a type of antibiotic that targets bacterial ribosomes and prevents protein production. Understand how they work and how resistance occurs.
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