Lab 35: Evalutation of Antiseptics: The Filter Paper Disk Method

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Sodium Hypochlorite
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Household bleach
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Antiseptics
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Substances such as alcohol or betadine that inhibit microbial growth or kill microorganisms, but are gentle enough to be applied to living tissue. Do not kill endospores; used for hand washing, treating surface wounds on the skin and preparing the skin for invasive procedures such as incisions and inoculations to prevent infections by opportunistic skin bacteria.
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Disinfectants
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Chemical agents that are applied to inanimate objects such as floors, walls and tabletops to kill microorganisms. More harsh than antiseptics, and therefore, are damaging to skin tissue.
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Sterilants or Sporocides
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Destroy all microbial life, including endospores.
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Ethylene Oxide
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Sterilant/sporocide – gas that is used to sterilize heat-sensitive objects (plastic petri plates, plastic pipettes, etc.)
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Sanitizers
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Agents that reduce microbial numbers to a safe level but do not completely eliminate all microbes. Are used in the food industry as on dishes, plates, equipment, etc.
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Bacteriostatic
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If a particular agent only inhibits the growth of bacterial cells but does not kill them. If the agent is removed, the growth of the bacterial cells would resume.
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Procedure
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1. Liquefy a nutrient agar pour in a water bath and cool to 50C. 2. Label the bottom of the petri plate with the names of the organism and chemical agent. 3. Inoculate the agar pour with a loopful of S. aureus and aseptically pour it into a sterile petri plate, allowing the medium to solidify. 4. Sterilize the forceps by dipping it in alcohol and flaming. Using the flamed forceps, pick up a sterile filter paper disk and dip it halfway int a disinfectant. Place the disk on the inoculated plate and gently press the disk onto the agar surface. Place no more than four disks on a 150mm plate. 5. Repeat with other testing bacteria. 6. Incubate the plates for 48 hours 37C.

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