The mechanism of antibiotics Biol 1220 Synthetic Biology

The mechanism of antibiotics Biol 1220 Synthetic Biology abe pressman & minoo ramanathan

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

sites of antiobiotic action

ampicillin • Belongs to β-lactam group of antibiotics – contain β-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?

ampicillin resistance • Cleavage of β-lactam ring by β-lactamase enzyme

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

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

Kanamycin • Targets 30 s 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

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 30 s subunit

chloramphenicol • Bacteriostatic: functions by halting bacterial growth, which is done by inhibiting the enzyme peptidyl transferase, a protein that assists in the binding of t. RNA to the 50 s ribosomal subunit • Three methods of resistance: reduced membrane permeability, mutation of the 50 s 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

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/Product. Detail. do? N 4=A 1593|SIAL &N 5=SEARCH_CONCAT_PNO|BRAND_KEY&F=SPEC • http: //abe. leeward. hawaii. edu/Protocols/Qiagen. Spinprep. Protocol. htm • http: //www. openwetware. org/wiki/Brown_BIOL 1220: Notebook/Syn. Bio_i n_Theory_and_Practice/Bacterial_Basics