Essay/Term paper: The effects of antibiotics on bacterial growth

Essay, term paper, research paper:  Biology

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 sun"s 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 don"t 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 Gram"s stain is as follows: the bacteria are stained with a
violet dye and treated with Gram"s 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 "plague", 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 synthesis of
the cell wall, proteins, or nucleic acids. Some antibacterials interfere with
the messenger RNA, consequently mixing up the bacterial genetic code.

Penicillins act by inhibiting the formation of a cell wall. This
antibiotic works most effectively against gram-positive streptococci,
staphylococci (e.g. Micrococcus Luteus) as well as certain gram-negative
bacteria. Penicillin is usually prescribed to treat syphilis, gonorrhea,
meningitis, and anthrax.

Tetracycline inhibits protein synthesis in pathogenic organism. This
antibiotic is obtained from the culture of Streptomyces.

Streptomycin an antibiotic agent which is obtained from Streptomyces
griseus. This antibiotic acts by limiting normal protein synthesis.
Streptomycin is effective against E. Coli, gram-negative bacilli, as well as
many cocci.

Neomycin an antibiotic derived from a strain of Streptomyces fradiae.
Neomycin effectively destroys a wide range of bacteria.

Kanamycin an antibiotic substance derived from Streptomyces kanamycetius.
Its antibacterial action is very similar to that of neomycin. Kanamycin works
against many aerobic gram-positive and gram-negative bacteria, especially E.
coli. Protracted use may result in auditory as well as other damages.

Erythromycin is an antibiotic produced by a strain of Streptomyces
erythreaus. This antibiotic works by inhibiting protein synthesis but not
nucleic synthesis. Erythromycin has inhibitory effects on gram-negative cocci
as well as some gram-positive bacteria.

Chloramphenicol is a clinically useful antibiotic in combating serious
infections caused by certain bacteria in place of potentially hazardous means of
solving the problem. In lab tests, it has been shown that this medicine stopped
bacterial reproduction in a wide range of both gram-positive and gram-negative
bacteria. The inhibition of cell reproduction caused by Chloramphenicol takes
place through interference with protein synthesis.

An experiment was conducted in order to determine which antibiotics are
most effective in inhibiting bacterial growth. First, the different bacteria
were placed on agar inside petri dishes. Then, antibiotic discs were placed into
the dishes. Each bacteria was exposed to every one of the antibiotics listed
above. The bacteria used in the experiment were: Bacillus Cerus, Escerichia
Coli, Seratia Marscens, and Micrococcus Luteus.

After a 24 hour incubation period, the results were measured. In order
to determine which antibiotic had the most effect their zones of inhibition were
recorded. The zone of inhibition refers to the distance from the disc to the
outermost section around the disc where no bacterial growth was present. The
results can be seen on the graph and data chart.

The following is a table showing the different zones of inhibition of each
antibiotic in the bacteria culture:
Tetracycline Chloramphenicol Kanamycin Neomycin
Penicillin Streptomycin Erythromycin B. Cerus 5.5 9 5
6.6 1 7 13
E. Coli 7
4.2 5.5 4.5 no effect 4.6 no effect
S. Marscens no
effect no effect 4.5 4 no effect 3 no effect
M. Luteus 23
22 10 11 23.5 11.5 19


After analysis of the data obtained it is obvious that each antibiotic
had a distinct effect on the growth of the different bacteria. The results of
this experiment are very important, since they teach of how each bacteria reacts
to different antibiotics. This is very valuable because it is the information
which assists physicians in prescribing certain medications to cure diseases
caused by bacteria.

Bibliography

1) Encart Encyclopedia 1994, CD-ROM. 2) McGraw-Hill Encyclopedia of Science and
Technology, 1992. 3) Physicians" Desk Reference, 1996.