Microbial Growth Control II - Antibiotics

  1. antimicrobial agent
    natural or synthetic chemical that kills or inhibits growth of microorganisms
  2. *bacteriostatic
    growth is inhibited, but cells are not killed
  3. *bacteriocidal
    cells are killed, but not lysed
  4. *bacteriolytic
    cells are killed and lysed
  5. *minimal inhibitory concentration (MIC)
    lowest concentration of an agent that completely inhibits growth
  6. *antibiotic assay by tube dilution
    • a series of decreasing concentrations of antibiotic is prepared in the culture medium
    • each tube is inoculated and incubation is allowed to proceed
    • growth occurs in tubes with concentrations below the MIC
  7. *Kirby-Bauer disk susceptibility test
    • add culture inoculated in liquid over nutrient agar plate
    • place antibiotic discs on surface
    • incubate
    • test organism shows sensitivity to some antibiotics, indicated by inhibition of bacterial growth around discs after incubation
    • compare zone of inhibition to standard chart

    • routinely used for testing antibiotic sensitivity in pathogens
    • generated antibiograms - indicated sensitivity of clinical ioslates
    • track emergence of antibiotic resistance strains of pathogens
  8. chemotherapeutic agents
    • antimicrobial agents used in vivo
    • can be synthetic, naturally occuring, or semi-synthetic
  9. growth factor
    • specific chemical substance required in the medium for growth of organism
    • organic compounds required in very small amounts and only by some cells
    • includes vitamins, amino acids, purines and pyrimidines
  10. growth factor analogs
    substance that is structurally similar to growth factor, but blocks utilization of the growth factor
  11. *selective toxicity
    inhibit bacteria or other pathogenic agents without adversely affecting host
  12. antimicrobials structure
    • diverse structures have anti-microbial activity
    • structural classification class can correlate with mode of action
    • very similar structures tend to have same mode of action, but may not
  13. antimicrobial spectrum of action
    • very specific spectrum of action - isoniazid
    • broad spectrum of action - tetracycline
  14. antimicrobials modes of action
    • bacteriostatic, -cidal, -lytic
    • targets: cell wall, cell membrane, DNA synthesis, RNA synthesis, protein synthesis, metabolism
  15. penicillin
    structure: b-lactam ring

    • mode of action:
    • inhibits transglycosylase and trans peptidase
    • bacteriolytic

    spectrum: most effective against gram positive bacteria
  16. gramicidin
    structure: cyclic peptide

    • mode of action:
    • forms cation channel that disrupts membrane polarity
    • bacteriolytic

    used topically on skin
  17. quinolone
    structure: quinolone

    • mode of action:
    • interact with bacterial DNA gyrase
    • prevent gyrase from supercoiling DNA and result in DNA with breaks
    • supercoiling is required for packaging of DNA in bacterial cell
    • DNA repair mechanisms are induced in uncoordinated fashion
    • irreversible damage to DNA and death
    • bacteriocidal

    • spectrum of action:
    • gram negative and positive bacteria
  18. sulfanilamide
    structure: PABA analog

    • mode of action:
    • growth factor analog (PABA)
    • blocks synthesis of DHF and folate
    • binds reversibly
    • bacteriostatic

    • spectrum of actvivity:
    • gram positive and negative bacteria
  19. tetracycline
    structure: napthacene ring system

    • mode of action:
    • reversibly binds to site on 30S ribosomal subunit
    • aminoacyl-tRNAs do not bind productively to the A site on the ribosome
    • inhibits protein synthesis
    • bacteriostatic

    spectrum of activity: broad
Card Set
Microbial Growth Control II - Antibiotics
general microbiology midterm 3