Zone of inhibition
Introduction:
Antimicrobial agents are chemicals that are used against bacteria. There are many such agents available. Because there are many different situations where bacterial control is important, no antimicrobial agent is effective in all situations. For example, you wouldn't use the same compound to fight an ear infection as you would use to sterilize surfaces in an
Operating room. The situations are completely different. In one case, you are trying to assist the body to fight off an internal, and in the other case, you are trying to eliminate bacteria from inanimate surfaces. There are many additional factors that you would have to consider in order to choose an appropriate antimicrobial agent for a given situation. For example, are the chemical properties of the agent (e.g., pH and solubility) appropriate for the situation? You would want to know whether the compound is toxic—to humans, other animals, plants, or beneficial bacteria. Finally, you would definitely want to know that the compound is effective against the organism(s) you are trying to eliminate. This project shows you one method of measuring the effectiveness of an antimicrobial agent against bacteria grown in culture. This is called the Kirby-Bauer disk-diffusion method, and here is how it works. The bacteria of interest are swabbed uniformly across a culture plate. Then a filter-paper disk, impregnated with the compound to be tested, is placed on the surface of the agar. The compound diffuses out from the filter paper into the agar. The concentration of the compound will be higher next to the disk, and will decrease gradually as distance from the disk increases. If the compound is effective against bacteria at a certain concentration, no colonies will grow wherever the concentration in the agar is greater than or equal to that effective concentration. This region is called the "zone of inhibition." Materials and Equipment:
• Samples of: Scalp, Ear, Feet, Nose, Arm, Underarm and
Antimicrobial agents are chemicals that are used against bacteria. There are many such agents available. Because there are many different situations where bacterial control is important, no antimicrobial agent is effective in all situations. For example, you wouldn't use the same compound to fight an ear infection as you would use to sterilize surfaces in an
Operating room. The situations are completely different. In one case, you are trying to assist the body to fight off an internal, and in the other case, you are trying to eliminate bacteria from inanimate surfaces. There are many additional factors that you would have to consider in order to choose an appropriate antimicrobial agent for a given situation. For example, are the chemical properties of the agent (e.g., pH and solubility) appropriate for the situation? You would want to know whether the compound is toxic—to humans, other animals, plants, or beneficial bacteria. Finally, you would definitely want to know that the compound is effective against the organism(s) you are trying to eliminate. This project shows you one method of measuring the effectiveness of an antimicrobial agent against bacteria grown in culture. This is called the Kirby-Bauer disk-diffusion method, and here is how it works. The bacteria of interest are swabbed uniformly across a culture plate. Then a filter-paper disk, impregnated with the compound to be tested, is placed on the surface of the agar. The compound diffuses out from the filter paper into the agar. The concentration of the compound will be higher next to the disk, and will decrease gradually as distance from the disk increases. If the compound is effective against bacteria at a certain concentration, no colonies will grow wherever the concentration in the agar is greater than or equal to that effective concentration. This region is called the "zone of inhibition." Materials and Equipment:
• Samples of: Scalp, Ear, Feet, Nose, Arm, Underarm and