The penicillins (pen-uh-SILL-ins) are a class of antibiotic
compounds derived from the molds Penicillium notatum and
Penicillium chrysogenum. The class contains a number of
compounds with the same basic bicyclic structure to which
are attached different side chains. That basic structure consists of two amino acids, cysteine and valine, joined to each
other to make a bicyclic (‘‘two-ring’’) compound. The different
forms of penicillin are distinguished from each other by
adding a single capital letter to their names. Thus: penicillin
F, penicillin G, penicillin K, penicillin N, penicillin O, penicillin
S, penicillin V, and penicillin X. A number of other
antibiotics, including ampicillin, amoxicillin, and methicillin,
have similar chemical structures.
Penicillin was discovered accidentally in 1928 by the
Scottish bacteriologist Alexander Fleming (1881–1995). Fleming
noticed that a green mold, which he later identified as
Penicillium notatum, had started to grow on a petri dish that
he had coated with bacteria. As the bacteria grew towards the mold, they began to die. At first, Fleming saw some promise
in this observation. Perhaps the mold could be used to kill
the bacteria that cause human disease. His experiments
showed, however, that the mold’s potency declined after a
short period of time He was also unable to isolate the antibacterial
chemical produced by the mold. He decided that
further research on Penicillium was probably not worthwhile.
As a result, it was not until a decade later that Penicillium’s
promise was realized. In 1935, English pathologist
Howard Florey (1898–1968) and his biochemist colleague
Ernst Chain (1906–1970) came across Fleming’s description
of his experiment and decided to see if they could isolate the
chemical product produced by Penicillium with anti-bacterial
action. They were eventually successful, isolating and purifying
a compound with anti-bacterial action, and, in 1941, began trials
with human subjects to test its safety and efficacy (ability to kill
bacteria). The successful conclusion of those trials not only
provided one of the great breakthroughs in the human battle
against infectious diseases, but also won for Florey, Chain, and
Fleming the 1945 Nobel prize for Physiology or Medicine.
Penicillins are classified as biosynthetic or semisynthetic.
Biosynthetic penicillin is natural penicillin. It is produced by culturing molds in large vats and collecting and
purifying the penicillins they produce naturally. There are
six naturally occurring penicillins. The specific form of penicillin
produced in a culturing vat depends on the nutrients
provided to the molds. Of the six natural penicillins, only
penicillin G (benzylpenicillin) is still used to any extent.
Semi-synthetic penicillins are produced by making chemical
alterations in the structure of a naturally occurring
penicillin. For example, penicillin V is made by replacing the
-CH2C6H5 group in natural penicillin G with a -CH2OC6H5
group.
Penicillins are prescription medications used to treat a
variety of bacterial infections, including meningitis, syphilis,
sore throats, and ear aches. They do so by inactivating an
enzyme used in the formation of bacterial cell walls. With the
enzyme inactivated, bacteria can not make cell walls and die
off. Penicillins do not act on viruses in the same way they do
on bacteria, so they are not effective against viral diseases,
such as the flu or the common cold.
A number of side effects are related to the use of penicillin.
These side effects include diarrhea, upset stomach, and
vaginal yeast infections. In those individuals who are allergic to penicillins, side effects are far more serious and include
rash, hives, swelling of tissues, breathing problems, and
anaphylactic shock, a life-threatening condition that requires
immediate medical treatment.
Penicillin may alter the results of some medical tests,
such as those for the presence of sugar in the urine. Penicillin
can also interact with a number of other medications,
including blood thinners, thyroid drugs, blood pressure
drugs, birth control pills, and other antibiotics, in some cases
decreasing their effectiveness.
Once promoted as wonder drugs, the use of penicillins
has declined slowly because of the spread of antibiotic resistance.
Antibiotic resistance occurs when new strains of bacteria
evolve that are resistant to existing types of penicillin.
One reason that antibiotic resistance has become a problem
is the extensive and often unnecessary use of penicillins.
When they are prescribed for colds and the flu, for example,
they have no effect on the viruses that cause those diseases,
but they encourage the growth of bacteria more able to
survive against penicillins.
