Chapter 10: Antimicrobial Drugs

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  1. The greatest number of antibiotics are derived from the following: (four)
    • Streptomyces (bacterium)
    • Bacillus (bacterium)
    • Penicillium (fungi)
    • Cephalosporium (fungi)
  2. Semi-Synthetics
    chemically altered antibiotics that are more effective than naturally occuring ones
  3. Synthetic Antibiotics
    Antimicrobials that are completely synthesized in a lab
  4. Prophylaxis
    • use of a drug to prevent imminent infection of a person at risk
    • not for use after the disease has occured
    • same as therapeutic drugs except in smaller dose
  5. Narrow Spectrum
    only effective against a very limited range of bacteria
  6. Broad Spectrum
    • targets something that is common between all different microbes
    • effect against a wide variety of microbes
  7. Selective Toxicity
    ability of an antimicrobial or drug to kill a microorganism but not harm the host (person)
  8. Characteristics of Ideal Antimicrobial Drug
    • Selective Toxicity
    • microbicidal (kill) rather than microbistatic (inhibits growth)
    • relatively soluble
    • remains potent long enough to work
    • doesn't lead to resistance
    • assists host's defenses
    • readily delivered to site of infection
    • reasonably priced
    • doens't disrupt host's health (allergies or other infections)
  9. Mechanisms of action of Microbial Drugs
    • Inhibition of Cell Wall synthesis
    • Inhibition of Protein synthesis
    • Disruption of cytoplasmic membrane
    • Inhibition of general metabolic pathway
    • Inhibition of DNA or RNA synthesis
    • Inhibition of pathogens attachment to, or recognition of host
  10. Inhibiton of Cell Wall synthesis
    • most common prevent cross-linkage of NAM subunits (beta-lactams)
    • bacteria have weekened cell walls and lyse
    • Beta-lactams
    • Vancomycin and cycloserine
    • Isoniazid and ethambutol
    • prevent bacteria from increasing amount of peptidoglycan, has no effect on existing layer, effective for only growing cells
  11. Beta-Lactams
    • more active aginst more types of bacteria
    • more stable in acidic enviroments
    • more readily absorbed
    • less susceptible to deactivation
    • **Simple beta lactams: Monobactams: effective only against gram-negatives
    • inhibit the last step in PGN synthesis, the transpeptidation reaction that cross-links the peptide side-chains of the polysaccharide-peptidoglycan backbone
  12. Vancomycin and Cycloserine
    interfere with particular bridges that link NAM subunits in many gram-posBacitracin- blocks secretion of NAG and NAM from cytoplasm
  13. Isoniazid and ethambutol
    Disrupt mycolic acid formation in mycobacterium species
  14. Bacitracin
    prevents the linkage of NAG and NAM and blocking their secretion from cytoplasm by binding the lipid carrier bactoprenol and preventing its dephosphorylation
  15. Phosphonomycin
    blocks the conversion of UDP-NAG to UDP-NAM by blocking pyruvyl transferase
  16. Cycloserine
    inhibits the activity of enzymes that add alanines to peptide side-chain
  17. Vancomycin
    inhibits both transglycosylation (NAM is attached to the NAG) and transpeptidation
  18. Inhibiton of Protein Synthesis
    • prokaryotic ribosome are 70S (30S and 50S)
    • eukaryotic ribosomes are 80S (40S and 60S)
    • Drugs: Aminoglycosides, tetracyclides, chloramphenicol, lincosamides, streptogramins, macrolides, fomiversen, oxazolidinones
  19. Aminoglycosides
    • cause change in 30S shape
    • mRNA is misread
  20. Tetracycline
    • block docking site of tRNA
    • blocks the A site of 30S
  21. Chloramphenicol
    blocks enzyme activity of the 50S subunit, preventing the formation of peptide bonds between AA
  22. Streptogramins
    • lincosamides or macrolides bind to 50S subunit, blocking proper mRNA movement through ribosome.
    • synthesis stops
  23. Formiversen
    blocks ribosomal sub units from attaching to mRNA
  24. Oxazolidinone
    • blocks initiation of translation
    • doesnt allow attachment
  25. Disruption of Cytoplasmic membranes
    • some drugs from channels through cytoplasmic membrane and damage it's integrity
    • nystatin and amphotericin B attach to ergosterol in fungal membranes
  26. Azoles
    • disruption of cyto membrane
    • inhibits ergosterol synthesis
  27. Polymyxin
    • disrupts cytoplasmic membranes of gram-negatives
    • toxic to human kidneys, because of this not prescribed often
  28. Pyrazinamide
    disrupts transport across cytoplasmic membrane of M.tuberculosis (very unique for treatment because most drugs act on mycolic acid)
  29. Parasitic Drugs: praziquantel and ivermectin
    act against cytoplasmic membranes by changing the permeability
  30. Inhibition of metabolic pathways
    • antimetabolic agents can be effective when pathogen and host's metabolic processes differ
    • Quinolones interfere with metabolism of malaria
    • heavy metal inactivates enzymes
    • drugs block activation of viruses
  31. Inhibition of Nucleic Acid synthesis
    • several drugs block DNA replication and mRNA transcription
    • drugs often affect both euk and prokaryotic cells
    • not normally used to treat infections
    • used in reseach and perhaps to slow cancer cell replication
  32. Nucleotide Analogs
    • intefere with function of nucleic acids
    • distort shapes of moleucles and prevent further replication, transcription, or translation
    • most often used against viruses
    • effective against rapidly dividing cancer cells
  33. Reverse transcriptase inhibitors
    • act against an enzyme HIV uses in it's replication cycle
    • do not harm people because humans lack reverse transcriptase
  34. Metronidazole
    when the nitro group enters the cells, it is reduced in the cytoplasm and forms cytotoxic compounds that disrupts the bacterial or protozoan DNA
  35. Minimum inhibitory concentration test
    • multiple tubes with increasing concentraion of antimicrobial
    • lower concentration will become turbid
    • first clear tube: will be minimum inhibitor
  36. Minimum bactericidal concentration test
    the concentration of the drug that was MIC (minimum inhibitory concentration) is innoculated on plate along with increasing concentrations to see whether bacterial colonies grew or not.
  37. Routes of Administration
    • Oral- requires no needles, self administered, takes longer
    • Intramuscular- via needle, takes a while to travel from muscle to bloodstream (not good for emergency)
    • Intravenous-delivers drugs directly to bloodstream
Card Set
Chapter 10: Antimicrobial Drugs
Chapter 10 of Microbiology Flash Cards for Exam 2
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