The Effect of Common Bactericidal Agents on Staphylococcus Epidermidis

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The Effect of Common Bactericidal Agents on Staphylococcus Epidermidis

Staphylococcus epidermidis is a facultative anaerobic bacterium. It is part of the normal human flora and is found on the skin. Colonies of these bacteria can produce a protective slime called a hydrophobic biofilm. Staphylococcus epidermidis is usually not pathogenic unless it enters the human body. One of the most common places for infections are hospitals where people often have weakened immune systems, open wounds or medical devices implanted in their bodies. Staphylococcus epidermidis can be fatal because of the protective biofilm and the bacteria’s resistance to common antibiotics makes the infection difficult to treat. This stresses the importance for hospitals to prevent infection by keeping a sterile environment.

There are many chemical agents that can be used to kill bacteria, but a hospital’s choices are limited by availability and cost of the agents. In this experiment the effectiveness of three common bactericidal agents, bleach, hydrogen peroxide, and isopropyl alcohol, were tested. This was done by creating aqueous solutions of staphylococcus epidermidis bacteria and a chemical agent. The solutions were then incubated on an agar petri dish for 24 hours. The quantity of staphylococcus epidermidis bacteria colonies that were grown were used as an indicator of how effective each agent was in killing the bacteria.

Each bactericidal agent has its own mechanism for killing bacteria. Both bleach and hydrogen peroxide are strong oxidizing agents, although hydrogen peroxide is a stronger oxidizing agent than hypochlorous acid, the oxidizing agent found in bleach. Oxidizing agents are very reactive compounds that take electrons away from other molecules to obtain a more stable form. When the oxidizing agents react with the bacteria they create free radicals which react with the lipids of the cell membrane. This reaction changes the molecular composition of the cell membrane causing an important part of the cell to cease functioning. The damage done to the bacteria is amplified by the products produced by the reaction. As the lipids are oxidized, they produce more free radicals and highly reactive compounds like aldehydes. These compounds along with the free radicals denature proteins and break apart DNA. The reaction results in cell death and destroys the bacteria’s ability to replicate.

The isopropyl alcohol is less reactive than the oxidizing agents, but still has the potential to kill bacteria cells. When the bacteria are exposed to an alcohol/ water mixture, the lipids in the cell membrane become soluble in water. This causes the cell membrane to fall apart and allows the alcohol to enter the cell. Once inside the cell, the alcohol can denature the proteins. Alcohol kills bacteria in a similar way as the oxidizing agents, by destroying the functionality of the cell membrane and proteins. However, isopropyl alcohol does not have the same damaging affect on DNA, nor does it have the ability to destroy bacterial spores like the strong oxidizing agents.

In this experiment in order to accurately determine the most effective bactericidal agent, the solutions that were compared were prepared containing the same concentration of the different chemical agents. The oxidizing agents are more reactive than the isopropyl alcohol , so if the reactivity(or the how easily the substance reacts with other substances)of the chemical agent determines the effectiveness in which the chemical agent in kills staphylococcus epidermidis, it was could be conjectured that the strong oxidative agents would be more effective than the isopropyl alcohol and the hydrogen peroxide would be the most effective bactericidal agent.

Methods and Results
In order to determine which chemical agent is most effective in killing staphylococcus epidermidis, solutions were made with the same concentration per volume. The chemical agents used were...
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