Antibiotics 1 Flashcards
What is selective toxicity?
The ability of a chemical substance to specifically target disease-causing organisms without harming the host.
Who coined the term ‘magic bullet’?
Paul Ehrlich.
What are chemotherapeutic agents?
Chemical substances that target and kill microbes or tumor cells, including antibacterial, antifungal, antiviral, antiretroviral, and anticancer drugs.
What is an antibiotic?
A substance produced by a microorganism that inhibits the growth of another microorganism at low concentrations.
What is the difference between bactericidal and bacteriostatic agents?
Bactericidal agents kill bacteria, while bacteriostatic agents inhibit their growth.
Give an example of a bactericidal antibiotic.
β-lactams or aminoglycosides.
Give an example of a bacteriostatic antibiotic.
Macrolides or tetracyclines.
What is the Minimum Inhibitory Concentration (MIC)?
The lowest concentration of an antibiotic that inhibits visible bacterial growth.
What is the purpose of Antimicrobial Susceptibility Testing (AST)?
To determine which antibiotics a pathogen is susceptible to and select appropriate treatment.
What are the key bacterial targets for antibiotics?
Ribosomes, DNA synthesis, RNA synthesis, cell wall, cell membrane, and biochemical pathways.
What is the mechanism of action for β-lactams?
β-lactams inhibit bacterial cell wall synthesis by binding to penicillin-binding proteins (PBPs), preventing the cross-linking of peptidoglycan chains which provides structural integrity to the bacterial cell wall. This ultimately leads to bacterial cell lysis.
How do β-lactamase inhibitors work?
β-lactamase inhibitors, like clavulanic acid, bind irreversibly to β-lactamase enzymes, preventing them from degrading β-lactam antibiotics and enhancing the efficacy of these antibiotics.
What is the mechanism of action for glycopeptides?
Glycopeptides, such as vancomycin, bind to the D-Ala-D-Ala terminus of peptidoglycan precursors, blocking the transpeptidation reaction required for peptidoglycan cross-linking, which is critical for cell wall integrity.
Why are glycopeptides only effective against Gram-positive bacteria?
Their large molecular size prevents penetration through the Gram-negative bacterial outer membrane, limiting their spectrum to Gram-positive bacteria.
What is the mechanism of action for aminoglycosides?
Aminoglycosides bind irreversibly to the 30S ribosomal subunit, causing misreading of mRNA and inhibiting protein synthesis, which is bactericidal.
What is the mechanism of action for tetracyclines?
Tetracyclines bind reversibly to the 30S ribosomal subunit, blocking the attachment of aminoacyl-tRNA to the ribosome and inhibiting protein synthesis, which is bacteriostatic.
What is the mechanism of action for macrolides?
Macrolides bind to the 50S ribosomal subunit, inhibiting translocation of the ribosome along the mRNA and blocking protein synthesis, which is bacteriostatic.
What is the mechanism of action for fluoroquinolones?
Fluoroquinolones inhibit bacterial DNA gyrase and topoisomerase IV, enzymes required for DNA replication and transcription, leading to bactericidal activity.
What is the mechanism of action for rifamycins?
Rifamycins inhibit bacterial RNA polymerase, blocking the synthesis of RNA and leading to bactericidal effects.
What is the mechanism of action for sulfonamides?
Sulfonamides inhibit dihydropteroate synthase, an enzyme involved in folate synthesis, which is essential for nucleotide production and bacterial growth.
What is the mechanism of action for polymyxins?
Polymyxins interact with the phospholipids of the bacterial cell membrane, disrupting its integrity and causing cell lysis, which is bactericidal.
What is the mechanism of action for lipopeptides like daptomycin?
Lipopeptides insert into the bacterial cell membrane in a calcium-dependent manner, causing membrane depolarization, ion leakage, and cell death.
What is the mechanism of vancomycin resistance?
Resistance to vancomycin occurs when the terminal D-alanine in the pentapeptide chain of peptidoglycan is replaced by D-lactate, reducing vancomycin binding affinity.
What is therapeutic drug monitoring (TDM) for vancomycin?
TDM involves adjusting vancomycin doses based on serum concentrations to achieve therapeutic efficacy while minimizing toxicity.
