Download antibiotics

Antibiotics
We all know what antibiotics are, right? Well, for the most part the “antibiotics” you’ve been
exposed to and hear about are actually antibacterial agents. But we’ll just stick with
“antibiotics.”
Microbes compete for food just like animals compete among one another and plants compete for
water, light, nutrients, etc. Microbes compete with one another by producing chemicals
(antibiotics) and releasing them into their environment. Fungi and bacteria both produce
antibacterial and antifungal compounds. Since Alexander Fleming discovered penicillin in 1928
(he got a Nobel Prize for it), hundreds of other compounds have been discovered. These
compounds go through rigorous testing to make sure they are safe for us to put in our bodies.
Many are not. The compounds that are safe for us (notwithstanding allergic reactions) target
bacterial cell functions in ways that are distinct from human metabolism. The way in which
antibiotics exert their effects varies, but most antibiotics on the market target one or the other of
2 different metabolic processes unique to bacteria. We refer to this as the mode of action. The
two most common (by far) are Cell Wall Synthesis Inhibition (CWSI) and Protein Synthesis
Inhibition (PSI). While antibiotics are produced by bacteria and fungi, it is common these days
for drug companies to chemically alter them in such a way that they are more effective. For
example, Amoxicillin is made from penicillin. It has a broader spectrum (kills more different
types of bacteria) than penicillin. But to make amoxicillin, you have to start with penicillin. We
call this partial synthesis. Many antibiotics are now made this way. There are several other
categories of Mode of Action, but we focus on the big two.
CWSIs: Bacterial cell walls are made of a hybrid polymer called peptidoglycan. This polymer is
found only in the cell walls of bacteria and no where else. Different CWSIs target different steps
in the pathways where peptidoglycan is made, but the effect is the same. No peptidoglycan.
PSIs: Bacterial ribosomes are fundamentally different from those found in Archaea or Eukara. If
a bacterium can’t make proteins, it will die. But these same compounds do not inhibit protein
synthesis in humans.
NOTE: The reason viruses are not harmed by antibiotics is that viruses are not cells, and
antibiotics interfere with cell function. It is not uncommon for doctors to prescribe antibiotics
for infections that are caused by viruses. The reason is that patients ask for them, and the doctor
may not be 100% certain if an infection is caused by bacteria or virus. Examples include
bronchitis and ear and sinus infections.
Our lab: We have recovered some gram + and gram – bacterial strains. We don’t know exactly
which strains they are, only whether they are gram + or gram -. Our lab will have two variables
(gram stain and mode of action). With 2 of each, that means we can compare the effect of CWSIs
with G+; CWSIs with G-; PSIs with G+; and PSIs with G-. As we often do, we will compile data
from all groups and classes to see what trends may emerge and what conclusions we can make.