1. Which version of iron would predominate in early Earth conditions? Explain why. Which version of iron predominates today? Explain why. Outline the process by which modern bacteria obtain iron and how they convert it into a form that they can metabolize.
2. How would a strain of Escherichia coli look under a microscope if it had a mutation that inactivated the protein MreB compared to a strain that had a fuctional MreB? Discuss two ways that the lack of functioning MreB can affect cell division. Hypothesize the problems a mutant bacterium would have if they were unable to produce functional Min proteins. Would this mutant be easy or difficult to isolate and grow? Explain.
3. The antibiotic penicillin interferes with transpeptidation of the peptidoglycan cell wall. In simple terms expain what this means. Give three reasons why this leads to lysis of the cell. During which phase of the bacterial growth curve would penicillin be most effective? Explain why.
4. Some gram negative bacterial cells are considered non-autolytic, which means they will not lyse or break down immediately after cell death. Diagram and label a growth curve comparing the log of the viable cells over time and a growth curve of the optical density of the sample over time. Explain the similarities and the differences you would see between the two curves.
5. Listeria monocytogenes infections are often transmitted through contaminated food. A person who has contracted listeriosis usually has a high fever, muscle aches, and gastrointestinal problems such as diarrhea. In severe cases meningitis can develop and the disease can be deadly. Refrigeration of food contaminated with this microbe does not prevent the transmission of the disease as the microbe can grow in refrigerator temperatures. How would you categorize Listeria based on its ability to grow in the refrigerator? Explain. Which temperature category would most pathogens fall into? Explain. Which temperature category or categories would you not expect to find any pathogen? Explain.
6. What will happen to the cells of Escherichia coli (an organism which normally grows in your intestine) if they were suddenly suspended in a solution of 20% NaCl? Explain. What would happen if the cells were suspended in distilled water? Explain. If growth nutrients were added to each cell suspension, which (if either) would support growth of the bacteria? Explain why or why not.
7. Which sterilization method would be the most efficient to sterilize nutrient agar that is to be used in the microbiology laboratory? Explain. If you needed to use nutrient agar with penicillin in it, would you be able to use this same sterilization method? Explain why or why not. If you also needed to disinfect your microbiology working surface which would be better able to lower microbial counts UV light or 50% ethanol solution? Explain
8. Where on your body would you expect xerotolerant normal flora to be found? Explain. Would these microbes also be halotolerant? Explain. What type of pH requirement would these microbes have? Explain. Under what situation would it be a benefit for a person to try and control this type of normal flora with the use of triclosan work? Why can the improper use of triclosan products be dangerous? How does triclosan work?
9. Coagulase is a virulence factor for Staphylococcus aureus that acts by causing clot formation at the site of S. Aureus growth. Streptokinase is a virulence factor for Streptococcus pyogenes that acts by dissolving clots at the site of S. pyogenes growth. Explain how these opposing strategies for enhancing pathogenicity can benefit each microbe. Streptokinase is often adminsistered during a heart attack. Why might this be the case? Would this cause an infection in the patient? Explain.
10. What is the typical pH of the adult female’s vagina? How is this pH maintained? Women who are on antibiotics can often develop a vaginal yeast infection. Explain why this can occur. How can their diet help prevent this from occurring? Explain.
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