The Effects of Antibiotics on Bacterial Growth


Biology II 1996

Bacteria are the most common and ancient microorganisms on earth. Most
bacteria are microscopic, measuring 1 micron in length. However, colonies of
bacteria grown in a laboratory petri dish can be seen with the unaided eye.

There are many divisions and classifications of bacteria that assist in
identifying them. The first two types of bacteria are archaebacteria and
eubacteria. Both groups have common ancestors dating to more than 3 billion
years ago. Archaebacteria live in environments where, because of the high
temperature, no other life can grow. These environments include hot springs and
areas of volcanic activity. They contain lipids but lack certain chemicals in
their cell wall. Eubacteria are all other bacteria. Most of them are
phototrophic, i.e. they use the sunís energy as food through the process of
photosynthesis.

Another classification of bacteria is according to their need of oxygen
to live. Those who do require oxygen to live are considered aerobes. The
bacteria who donít use oxygen to live are known as anaerobes.

The shape of specific bacteria provides for the next step in the
identification process. Spherical bacteria are called cocci; the bacteria that
have a rodlike shape are known as bacilli; corkscrew shaped bacteria are
spirilla; and filamentous is the term for bacteria with a threadlike appearance.

Hans Christian Joachim Gram, a Danish microbiologist, developed a method
for distinguishing bacteria by their different reaction to a stain. The
process of applying Gramís stain is as follows: the bacteria are stained with a
violet dye and treated with Gramís solution (1 part iodine, 2 parts potassium
iodide, and 300 parts water). Ethyl alcohol is then applied to the medium; the
bacteria will either preserve the blue color of the original dye or they will
obtain a red hue. The blue colored bacteria are gram-positive; the red bacteria
are identified as gram-negative.

Bacteria contain DNA (deoxyribonucleic acid) just like all cells.
However, in bacteria the DNA is arranged in a circular fashion rather than in
strands. Bacteria also contain ribosomes which, like in eukaryotic cells,
provide for protein synthesis. In order for a bacterium to attach itself to a
surface, it requires the aid of pili, or hairlike growths. Bacteria, just like
sperm cells, have flagella which assist in movement. But, sperm cells only have
one flagellum, whereas bacteria contain flagella at several locations throughout
their body surface.

Although most bacteria are not harmful, a small fraction of them are
responsible for many diseases. These bacterial pathogens have affected humans
throughout history. The ďplagueĒ, an infamous disease caused by bacteria, has
killed millions of people. Also, such a disease as tuberculosis, a disease
responsible for the lives of many, is caused by bacterial pathogens ingested
into the body.

Bacteria affect everyone in their daily life because they are found
nearly everywhere. They are found in the air, in food, in living things, in
non-living things, and on every imaginable surface.

Escherichia coli is a disease causing gram-negative bacillus. These
bacteria are commonly found within the intestines of humans as well as other
vertebrates. This widely spread bacteria is known to cause urinary tract
infections as well as diarrhea.

Microcococcus Luteus are gram-positive parasitic spherical bacteria
which usually grows in grapelike clusters. This species is commonly found in
milk and dairy products as well as on dust particles.

Bacillus Cereus are a spore forming type of bacteria. They are gram-
positive and contain rods. Due to the fact that this bacteria is known to
survive cooking, it is a common cause of food poisoning and diarrhea.

Seratia Marscens a usually anaerobic bacteria which contains gram-
negative rods. This bacteria feeds on decaying plant and animal material. S.
marscens are found in water, soil, milk, foods, and certain insects.

In spite of the fact that bacteria are harmful to the body, certain
measures can be taken in order to inhibit their growth and reproduction. The
most common form of bacteria fighting medicines are antibiotics. Antibiotics
carry out the action which their Greek origin suggests: anti meaning against,
and bios meaning life. In the early parts of the 20th century, a German chemist,
Paul Ehrlich began experimentation using organic compounds to combat harmful
organisms without causing damage to the host. The results of his
experimentation began the study and use of antibiotics to fight bacteria.

Antibiotics are classified in various ways. They can be arranged
according to the specific action it has on the cell. For example, certain
antibiotics attack the cell wall, others concentrate on the cell membrane, but
most obstruct protein synthesis. Another form of indexing antibiotics is by
their actual chemical structure.

Practically all antibiotics deal with the obstruction of