Introduction to antimicrobial drugs Flashcards
What is the primary target of antibacterial drugs?
The primary target of antibacterial drugs is bacterial metabolic processes, which exploit biochemical differences between pathogens and the host to selectively target bacteria without harming human cells.
Why are sulphonamides and trimethoprim effective against bacteria?
Sulphonamides and trimethoprim are effective because they target the folate biosynthetic pathway in bacteria. Bacteria must synthesize folate from scratch, while humans obtain it from their diet. These antibiotics block key steps in folate production, preventing bacterial growth.
How does trimethoprim differ from sulphonamides in terms of side effects and uses?
Trimethoprim has fewer side effects compared to sulphonamides and is commonly used for urinary tract infections. It is a broad-spectrum antibiotic that affects a wide range of bacteria, including both Gram-positive and Gram-negative species, as well as aerobes and anaerobes.
What is the role of peptidoglycan in bacterial cells?
Peptidoglycan forms the bacterial cell wall, providing mechanical strength and supporting the underlying plasma membrane. It helps bacteria survive in environments with varying osmotic pressures and prevents the cell from bursting due to osmotic imbalance.
How do antibiotics like penicillin and cephalosporins target bacterial cells?
Penicillin and cephalosporins target the bacterial cell wall, specifically the peptidoglycan structure. These antibiotics are particularly effective against Gram-positive bacteria, as they weaken the cell wall, causing the bacteria to burst (lysis) under different osmotic conditions.
Why are bacterial ribosomes targeted by antibiotics like chloramphenicol?
Bacterial ribosomes are targeted because they differ from human ribosomes in structure. Bacterial ribosomes consist of 50s and 30s subunits, whereas human ribosomes have 60s and 40s subunits. Antibiotics like chloramphenicol inhibit bacterial protein synthesis by blocking transpeptidation, which leads to premature termination of the peptide chain.
How do antibiotics like fluoroquinolones affect bacterial nucleic acid synthesis?
Fluoroquinolones and other antibiotics affect bacterial nucleic acid synthesis by inhibiting DNA gyrase, an enzyme responsible for uncoiling supercoiled DNA, which is necessary for transcription. These antibiotics are particularly effective against Gram-negative bacteria.
What makes antibacterial drugs effective without harming the host?
Antibacterial drugs are designed to exploit biochemical differences between bacteria and the host, targeting bacterial processes that do not exist or function differently in human cells. This selectivity minimizes harm to the host while effectively killing or inhibiting bacterial growth.
What role does peptidoglycan play in the bacterial cell wall?
Peptidoglycan provides structural support and strength to the bacterial cell wall, allowing bacteria to survive environmental conditions with fluctuating osmotic pressure. It prevents the bacterial cell from bursting when exposed to different osmotic environments.
Why are sulphonamides considered early antibiotics with serious side effects?
Sulphonamides block folate synthesis in bacteria, inhibiting bacterial growth. However, they can cause serious adverse reactions in humans, which is why they are now reserved for use in only very serious infections.
How does the folate biosynthetic pathway differ in bacteria and humans?
Bacteria must synthesize folate from scratch, whereas humans obtain folate from their diet. This difference allows drugs like sulphonamides and trimethoprim to specifically target bacterial folate production without affecting human folate metabolism.
What is the advantage of combining sulphonamides and trimethoprim for treatment?
When used together, sulphonamides and trimethoprim provide a more complete blockage of folate metabolism in bacteria, enhancing their effectiveness in stopping bacterial growth and even killing the bacteria.
How do penicillin and cephalosporins target bacteria?
Penicillin and cephalosporins target the bacterial cell wall, specifically the peptidoglycan layer. This weakens the cell wall, causing the bacteria to burst (lysis) under osmotic pressure. These antibiotics are particularly effective against Gram-positive bacteria.
Why are Gram-negative bacteria harder to treat with antibiotics like penicillin?
Gram-negative bacteria have an additional outer membrane that makes it harder for antibiotics like penicillin to penetrate the cell wall. The cell wall is also thinner compared to Gram-positive bacteria, making it less susceptible to damage from penicillin.
What is the significance of bacterial ribosomes in antibiotic targeting?
Bacterial ribosomes differ in structure from human ribosomes, with bacterial ribosomes having 50s and 30s subunits, whereas human ribosomes consist of 60s and 40s subunits. This difference makes bacterial ribosomes a key target for antibiotics like chloramphenicol, which inhibits protein synthesis in bacteria.
How does chloramphenicol inhibit bacterial protein synthesis?
Chloramphenicol blocks transpeptidation during protein synthesis, which prevents amino acids from linking together and causes premature termination of the peptide chain. This disrupts the production of proteins necessary for bacterial growth.
How do antibiotics affect bacterial nucleic acid synthesis?
Antibiotics can interfere with bacterial nucleic acid synthesis by inhibiting enzymes like DNA polymerase or RNA polymerase, altering DNA base-pairing properties, or blocking nucleotide synthesis. This disrupts DNA replication and protein synthesis, preventing bacterial reproduction.
Why are fluoroquinolones particularly effective against Gram-negative bacteria?
Fluoroquinolones target DNA gyrase, an enzyme that uncoils supercoiled DNA for transcription and replication. This action is especially effective against Gram-negative bacteria, which rely heavily on DNA gyrase for their replication process.
What is the difference between Gram-positive and Gram-negative bacteria in terms of antibiotic susceptibility?
Gram-positive bacteria have a thick cell wall made of peptidoglycan, which is more easily targeted by antibiotics like penicillin and cephalosporins. Gram-negative bacteria, on the other hand, have an additional outer membrane that protects the cell wall, making them more resistant to certain antibiotics.
Why are broad-spectrum antibiotics like trimethoprim effective against a wide range of bacteria?
Trimethoprim is a broad-spectrum antibiotic because it interferes with the bacterial folate biosynthesis pathway, which is essential for DNA synthesis in both Gram-positive and Gram-negative bacteria. By blocking folate metabolism, trimethoprim inhibits bacterial growth across a wide range of bacterial types, including both aerobes and anaerobes.
