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

Household bleach

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.

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.

Destroy all microbial life, including endospores.

Sterilant/sporocide - gas that is used to sterilize heat-sensitive objects (plastic petri plates, plastic pipettes, etc.)

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.

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.

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.