The overwhelming majority of antibiotic substances are natural products that certain bacteria and fungi (molds) produce and send outside of their cells. About 90% of the antibiotics in use today, are isolated from bacteria. There are a few antibiotics, however, which are completely synthetic... that is, are made from scratch in the laboratory. These particular antibiotics are designed to inhibit some process previously identified to be completely unique to bacteria, and necessary for the bacterium to remain alive.
For a bacterium or a fungus living out in the wild, if they can make
something that removes or drastically "slows-down" the
competition for the available nutrients, then they'll have an advantage.
So, even though these microorganisms don't have the ability to decide what
to make... through mutations and other events, it is possible for them to
acquire such an ability to compete.. then, it is these organisms which
survive more readily within the environment. We use antibiotics for a
different reason, of course, that is, to help us kill harmful bacteria
that cause infection and disease. To determine which antibiotic works
best against a given bacterium, tests are done in the laboratory, just
like the one below:
My special thanks to Raymond Lin for his permission to use the antibiotic sensitivity-plate image you see to the left of this text. A drop of liquid is removed from a culture of the bacterial cells in suspension, and the drop is placed on a Petri dish containing agar and nutrients. A sterile glass rod, bent at a 90-degree angle, is then used to spread the drop all over the surface of the agar (a spread plate). Then,small, circular, sterile discs, each saturated with a different antibiotic are dropped on the plate, equi-distant from one another. The plate is then incubated at an appropriate temperature, and one looks for zones around each disc where no growth is occurring (bacteria sensitive). If the bacterium is resistant to a given antibiotic, growth will occur all around the disc.
When taking an antibiotic, it is very important to follow all instructions from your physician and pharmacist, to the letter. While at the proper dosage most antibiotics will not hurt us, there can sometimes be harmful side-effects. Some people are allergic to a given antibiotic - allergies to penicillin or its derivatives, are relatively more common. In this case, there are other antibiotics - like cephalosporin, for example, which may be used as a substitute. And, sometimes certain types of antibiotics, like streptomycin, can cause damage to the nerves involved with balance and hearing (8th cranial nerve - vestibular and auditory branches, respectively). Therefore, after taking an antibiotic, if you experience any one of the following symptoms: feel sick to your stomach, acquire a rash, feel dizzy, or hear "ringing" in your ears, call your physician right away. Any children taking an antibiotic, should therefore be carefully monitored for any of the above symptoms.
One of the major problems we now face, is that many of the disease-causing bacteria that we know of (like staphylococcus - "staph"), have become resistant to the effects of different antibiotics. This resistance appears when a member of the bacterial population (need be only a single cell) genetically acquires the ability to destroy the antibiotic. Then, although all other members of the bacterial population may be killed, this one resistant cell will divide (as often as every 20 minutes in some cases) and produce a population that is now no longer harmed. This concern is great, because certain strains of disease-causing bacteria now have only one antibiotic remaining which will kill them. Because of this concern, there are significant efforts to find new natural sources of antibiotics, or to make completely synthetic ones in the laboratory. It is for this reason that physicians may hesitate to prescribe a certain antibiotic until it is clear that it is absolutely necessary. One of the reasons this problem now exists, is because of our prior, indiscriminate use of antibiotics in human and domestic animal health (particularly cattle and pigs). In some countries of the world, one still does not need a prescription to use an antibiotic - one may purchase them just as one may purchase aspirin.
Sometimes, we can determine exactly what an antibiotic looks like, and we can chemically add or remove some things from the original structure, and produce an altered form of the original material. This new, altered, substance is called a semi-synthetic antibiotic. These chemical changes are sometimes made to make the antibiotic last longer in our bodies. I'm sure that you are familiar with the antibiotic, penicillin, and the semi-synthetic form called Ampicillin. Penicillin is produced by a particular kind of fungus (Penicillium - a kind of fungus that can grow on bread). However, penicillin is very sensitive to stomach acid, and will be broken-down before it can do any good. It is for this reason that penicillin is given with a shot. A semi-synthetic derivative, called Ampicillin, has therefore been made, because this form is resistant to stomach acid - is why one can take Ampicillin in tablet form (better, huh?).
Back in 1929, penicillin was re-discovered by a Scottish researcher named
Alexander Fleming (penicillin was originally discovered by a French
medical student by the name of Duchesne). An article about penicillin and
its action on bacteria can be accessed from "What the Heck
Is...", or, you can access directly via this link:
What the Heck Is Penicillin?
It wasn't until 1941 in England, that an Australian (Howard Florey) and an Englishman (Ernst Chain) developed commercial methods to produce penicillin for human use. The TOTAL amount of penicillin available for use in the clinical trial on humans at that time, was LESS THAN the amount one would receive in a single shot, today! At that time, of course, World-War II was in progress, and there was a major effort to try to make penicillin available to all of the British, U.S., and other allies involved with fighting Germany, Japan, and Italy. Because England did not have the industrial capacity necessary for large-scale production, nor protection from bombing raids, the entire process was moved to the United States. It is for this reason primarily, that the pharmaceutical industry became so well-established in the U.S. Initially, only military personnel were allowed access to this life-saving material. Eventually, prior to the end of World-War II, penicillin was made available to the general public.
Luckily for me, on my death-bed suffering from measles (a virus) and from
bacterial pneumonia as a child in 1944, I was allowed to have penicillin
because my father was in the Army - saved my life. Thank you, Drs
Fleming, Florey, and Chain for your wonderful science.
You may wish to look at the action of this antibiotic. Please see Jim Sullivan's Cells Alive! information and look at the effect penicillin has on a dividing bacterium: