The mechanism of antibiotics

1
The mechanism of antibiotics

• Biol 1220 Synthetic Biology
• abe pressman minoo ramanathan

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the basics

• Used to kill or inhibit the growth of bacteria
• Classified as bactericidal or bacteriostatic
• Kill bacteria directly Prevent cell division
• Classified by target specificity
• Narrow-spectrum vs Broad range
• Most modified chemically from original compounds
  found in nature, some isolated and produced from
  living organisms

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sites of antiobiotic action
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ampicillin

• Belongs to ß-lactam group of antibiotics
  contain ß-lactam ring
• Broad-spectrum
• Penicillin derivative that inhibits bacterial
  cell wall synthesis (peptidoglycan cross-linking)
  
• Inactivates transpeptidases on the inner surface
  of the bacterial cell membrane
• Bactericidal only to growing E. Coli
• Widespread use leads to bacterial resistance.
  HOW?

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ampicillin resistance

• Cleavage of ß-lactam ring by ß-lactamase enzyme

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ampicillin resistance

• ß-lactamase is encoded by the plasmid-linked bla
  (TEM-1) gene
• Hydrolyzes ampicillin
• Ampicillin levels in culture continually depleted

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use in synthetic biology

• To confirm uptake of gene (eg. of plasmids) by
  bacteria
• Bacterial Transformation DNA integrates into
  bacterias chromosome and made chemically
  competent
• Exogenous DNA tagged with an antibiotic
  resistance gene eg. ß-lactamase
• Grown in medium containing ampicillin
• Ampicillin resistance indicates successful
  bacterial transformation

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Kanamycin

• Targets 30s ribosomal subunit, causing a
  frameshift in every translation
• Bacteriostatic bacterium is unable to produce
  any proteins correctly, leading to a halt in
  growth and eventually cell death

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kanamycin use/resistance

• Over-use of kanamycin has led to many wild
  bacteria possessing resistance plasmids
• As a result of this (as well as a lot of side
  effects in humans), kanamycin is widely used for
  genetic purposes rather than medicinal purposes,
  especially in transgenic plants
• Resistance is often to a family of related
  antibiotics, and can include antibiotic-degrading
  enzymes or proteins protecting the 30s subunit

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chloramphenicol

• Bacteriostatic functions by halting bacterial
  growth, which is done by inhibiting the enzyme
  peptidyl transferase, a protein that assists in
  the binding of tRNA to the 50s ribosomal subunit
• Three methods of resistance reduced membrane
  permeability, mutation of the 50s subunit, and an
  enzyme called chloramphenicol acetyltransferase,
  which inactivates chloramphenicol by covaltly
  linking groups
• Easy/cheap to manufacture, but unused in western
  countries because of possible aplastic anemia as
  a side effect

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Sources

• http//en.wikipedia.org/wiki/Antibiotic
• http//en.wikipedia.org/wiki/Ampicillin
• http//en.wikipedia.org/wiki/Beta-lactamase
• http//www.sigmaaldrich.com/catalog/ProductDetail.
  do?N4A1593SIALN5SEARCH_CONCAT_PNOBRAND_KEYF
  SPEC
• http//abe.leeward.hawaii.edu/Protocols/QiagenSpin
  prepProtocol.htm
• http//www.openwetware.org/wiki/Brown_BIOL1220Not
  ebook/SynBio_in_Theory_and_Practice/Bacterial_Basi
  cs