———————————————————— Lab 9 ————————————————————

Effectiveness of Common Household Antimicrobial Cleaning AgentsTheory:

There are many choices available when it comes to cleaning products. This lab will give you the chance to test common cleaners against two types of common bacteria. Not every antimicrobial solution kills/inhibits bacterial growth in the same way. Additionally, effectiveness is generally far more dependent upon the concentration of the product used rather than the type of organism being targeted. There are two major types of cleaners:

Bacteriostatic: These cleaners slow the growth of microorganisms.Bactericidal: These cleaners kill microorganisms. It is very possible for a drug, chemical or cleaning solution to be bacteriostatic at low

concentrations, but once it reaches a certain higher concentration that same drug, chemical or cleaning solution becomes bactericidal. The same is true for the concentration needed to achieve bacteriostatic conditions. This means at really low concentration, a drug, chemical or cleaning solution might have no effect on microbial growth at all.

This lab is one method by which antibacterial products are tested against their claims. It also is a way to look at what minimum concentration of the product is needed to accomplish those claims. In many cases, some products perform well even when diluted. A solution is considered statistically effective if it prevents the growth of targeted microbes at least 95% of the time. Too strong a concentration can lead to side effects for the user. Other unintended consequences may include harmful fumes or itchy rashes. You will test one bacteria of your choice versus the product at your table—which is represented in 3 different concentrations (full strength, 10% strength, and 1% strength). A negative and positive control will also be prepared and used for comparison purposes in the next lab.

We will infect glass beads with bacteria then allow them to soak in various concentrations of cleaner. In the next lab you will determine if the cleaner killed all the bacteria or not. A tube of clear solution (like the negative control) means there was no growth. The cleaning agent was bactericidal at the concentration used and the time exposed. A tube of cloudy solution (like your positive control) means there was bacterial growth. The cleaning agent was either ineffective or bacteriostatic at the concentration used and the time exposed.

Procedure: Lab Materials:1. Label each of your 5 nutrient broth test tubes with your last name. (We’ll

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Each student should obtain the following:

5 Tubes of Sterile Nutrient Broth5 Sterile Glass Beads1 Pair Forceps1 Beaker of Ethanol1 Bunsen Burner3 Petri Dishes of a Cleaner in Varying Concentrations1 Test Tube of either Escherichia coli or Staphylococcus aureus

know the lab section & date by the rack they are in.) Each test tube should also include one of the following labels:

- negative control - positive control- _______ % of ___________

(for example, 100% bleach)- ________ % of __________

(for example, 10% bleach)- ________ % of __________

(for example, 1% bleach)

1. Dip the end of your forceps into the beaker of Ethanol to sterilize them. Light the Ethanol with the Bunsen Burner and allow the flame to burn out. DO NOT BLOW THE FLAME OUT, as this will infect your forceps.

2. Using sterile technique, transfer 1 sterile bead to your negative control tube with the sterilized forceps.

3. Dump the bacterial tube’s contents into the Petri dish containing the other 4 glass beads and gently roll them around in the petri dish (with the lid on) to coat them with the bacteria.

4. Using sterile forceps and sterile technique, transfer 1 glass bead to the positive control test tube.

5. Using sterile forceps and sterile technique, transfer 1 glass bead to each of the 3 Petri Dishes provided, the contents of which should match what you wrote on the 3 remaining test tubes.:

Cleaning Solution ____________________ at ______% concentration.Cleaning Solution ____________________ at ______% concentration.Cleaning Solution ____________________ at ______% concentration.

6. Soak in Petri dish for 10 minutes each, then perform a sterile transfer of each glass bead to a sterile tube of nutrient broth with the forceps. Be sure to re-sterilize your forceps each time and allow it to properly cool! Also, be sure to place the bead into the tube with the proper label!To avoid cross-contamination and potential accidents in the procedure, transfer each bead slowly. If you drop a bead let me know!

7. Put your 5 tubes in the designated test tube rack for storage until the next lab. Any test tubes that remain clear (like the negative control) is bacteria free, whereas a cloudy tube (like the positive control) has bacterial growth.

Lab 9 Questions (Due at the end of lab)

Name: __________________________________________________ Grade: _______ of 10 pointsBe sure to explain thoroughly and use complete sentences.

1. (1 point) Name of bacteria:Page 2 of 4

2. (1 point) Name of cleaning product:

3. (2 points) If a certain concentration of a cleaning product is only partially effective, what might that tube of nutrient broth look like in the next lab? Is this concentration bacteriostatic or bactericidal? Explain.

4. (3 points) Indicate three other factors other than the concentration of the cleaning agent that can be tested to determine the impact they have on antimicrobial activity. Explain or provide an example for each.

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5. (3 points) The Minimum Inhibitory Concentration (MIC) is the lowest concentration at which a drug or cleaning agent prevents visible growth of bacteria. In the photo below, what range of concentration is the MIC in? If the concentrations of 13.0mcg and higher are known to cause skin rashes, then what range of concentrations

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are considered both safe and effective? Be sure to provide an explanation for both answers.

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