Lab 5: Growth of Microorganisms (100 points)

• Each question on the lab worksheet must be answered completely, thoroughly, in complete sentences and correctly in order to be considered for full credit
• If the question asks you to do research or find a source, a reputable, credible and/or scholarly source citation must be included in order to be considered for full credit
• If a math formula is required to arrive to an answer, work must be shown otherwise, no credit will be awarded

Pre-Lab Questions

1. Why don’t microorganisms in cultures exhibit constant exponential growth? What are some steps you could take to extend the lifespan of a microbial culture? (5 points)
2. Using a textbook or a reputable online source, describe how lab cultures are maintained in a continual pattern of growth. Focus particularly on those used in biotechnology, such as E. coli, which is used to make human insulin. (5 points).
3. What are the four phases of bacterial growth in a closed system? (5 points)
4. What are the physical and chemical methods of microbial control and what are the two methods used? (5 points).
5. You are a physician trying to isolate bacterial colonies from the human gut in attempt to diagnose a gastrointestinal infection. You streak your sample on a growth media containing glucose, amino acids, and salts that contain both sulfur and phosphorous with a pH of 7. You incubate the plates in aerobic conditions at 37 ˚C for three days, at which point you can see clear bacterial colonies forming on the plate.

.Experiment 1 Results Tables Table 1: Experiment 1 Results (10 points)

Experiment 1 Post-Lab Questions

1. What does the pink band in the FTM indicate? (5 points).
2. What would be the effect of using FTM tubes with a broad pink zone? (5 points).
3. Provide an explanation as to why bacteria from each location displayed their pattern of growth. Are there any results that surprise you? If so, why? (5 points).
4. Why is it important to pull the inoculating needle out of the FTM via the same path you inserted it? (5 points).
5. Why was it necessary to have separate controls for the agar plates and the FTM tubes? (5 points).
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Experiment 2 Results Tables

• Table 2: Experiment 2 Results (10 points)

Experiment 2 Post-Lab Questions

1. Which germicide was most effective for each sample? Was the same germicide the most effective for microorganisms isolated from the different sources?
2. Which germicide was least effective? Was the same germicide the least effective for microorganisms isolated from the different sources? What could explain this similarity or difference? (5 points).
3. Were any of the cultured microorganisms particularly resistant to the germicides tested? If so, which culture? What could explain this strong resistance? (5 points).
4. What was the purpose of the dipped piece of filter paper in deionized water plate? (5 points).
5. Research the chemical formulas for bleach, isopropyl alcohol, and chlorhexidine gluconate (the active ingredient in Hibiclens®). How does each chemical achieve its germicidal properties on the molecular level? (5 points).
6. What are some real-world applications for a study like this? For instance, how would these results influence cleaning practices in a doctor’s office or treatment of a disease? (5 points).