have played a major role in our society thanks to Sir
Alexander Fleming's careful observations in 1928. Without it, many lives
would be in danger due to infectious diseases.
Antibiotics are chemical substances produced by various species of
microorganisms and other living systems that are capable in small
concentrations of inhibiting the growth of or killing bacteria and other
microorganisms. These organisms can be bacteria, viruses, fungi, or
animals called protozoa. A particular group of these agents is made up of
drugs called antibiotics, from the Greek word anti ("against") and bios
("life"). Some antibiotics are produced from living organisms such as
bacteria, fungi, and molds. Others are wholly or in part synthetic - that
is, produced artificially.

Penicillin is perhaps the best known antibiotic. Its discovery and
later development is among mankind's greatest achievements. Antibiotics
have enabled the medical profession to treat effectively many infectious
diseases, including some that were once life-threatening.

How Antibiotics Work ?

Antibiotics can be bacteriostatic (bacteria stopped from multiplying)
or bactericidal (bacteria killed). To perform either of these functions,
antibiotics must be brought into contact with the bacteria.

It is believed that antibiotics interfere with the surface of bacteria
cells, causing a change in their ability to reproduce. Testing the action
of an antibiotic in the laboratory shows how much exposure to the drug is
necessary to halt reproduction or to kill the bacteria. Although a large
amount of an antibiotic taken at one time might kill the bacteria causing
an illness, such a dose usually would make the person suffer from illness
caused by the drug. Therefore, antibiotics are given in a series of
smaller amounts. This assures that the bacteria are either killed or
reduced enough in numbers so that the body can repel them. When too little
antibiotic is taken, bacteria can often develop methods to protect
themselves against it . The next time the antibiotic is needed against
these bacteria, it will not be effective.

Taking in Antibiotics.

To work against infecting organisms, an antibiotic can be applied
externally, such as to a cut on the skin's surface, or internally, reaching
the bloodstream within the body. Antibiotics are made in several forms and
given in different ways.

Topical. Topical application means "to a local area" such as on the
skin, in the eyes, or on the mucous membrane. Antibiotics for topical use
are available in the form of powders, ointments, or creams.

Oral. Tablets, liquids, and capsules are swallowed. The antibiotic
is released in the small intestine to be absorbed into the bloodstream.
Troches, or lozenges, are allowed to dissolve in the mouth, where the
antibiotic is absorbed through the mucous membrane.

Parenteral. Applications outside the intestine are called parenteral.
One form is an injection, which can be subcutaneous (under the skin),
intramuscular (into a muscle), or intravenous (into a vein). Parenteral
administration of an antibiotic is used when a physician requires a strong,
quick concentration of the antibiotic in the bloodstream.

Manufacture.

Natural. At one time all antibiotics were made from living organisms.
This process, known as biosynthesis, is still used in the manufacture of
some antibiotics. It is actually the organisms that manufacture the
antibiotic. The people involved merely provide favorable conditions for
the organisms to do the work and then they collect the drug. For example,
mold organisms are placed in a medium (a substance used for the growth of
microorganisms) such as corn steep liquor to which milk sugar has been
added. This forms a broth that is put into a tank, which is kept at a
temperature of 25'C and shaken for more than 100 hours. The mold organisms
grow rapidly in this warm soup, producing penicillin as they do so. The
penicillin is later extracted.

Synthetic. All penicillin types have an identical chemical nucleus
called a ring. The chemical chain that is attached to the ring is
different in each type. By changing the molecules of the chain, scientists
devise drugs with potentially different effects on different organisms.
Some of these drugs are useful in treating infections, some are not.

Pharmaceutical manufacturers now use computer-generated images of the
rings and experiment with an endless variety of possible chains.
Researchers have developed antibiotics with long half- lives (period of
effectiveness), which allow taking the medication once in 24 hours instead
of every few hours. The newer antibiotics are also more effective against
a wider range of infections than were earlier drugs.

Varieties of Antibiotics.
There are dozens of antibiotics. The following are in common use:

Penicillins. The various types of penicillins make up a large group
of antibacterial antibiotics of which only those from benzyl penicillin are
naturally produced from molds. Penicillin G ...