The Effects of Antibiotics on Bacterial Growth

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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...
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