Review Questions for Chapter 5: Control of Microbial Growth
1. Consider the following statement: âThorough handwashing with soap and water is the most important step in stopping the spread of many infectious diseasesâ.
a. Explain this statement.
b. Following thorough handwashing with soap, are your hands sterile? Why or why not?
2. If pasteurization does not achieve sterilization, why is pasteurization used to treat food? Why not just heat the food instead?
3. Consider the use of salts and sugars to preserve food.
a. How do salts and sugars preserve foods?
b. Why are these considered physical rather than chemical methods of microbial control?
c. Name one food that is preserved with sugar and one preserved with salt.
d. How do you account for the occasional growth of Penicillium mold in jelly, which is 50% sucrose?
4. Consider dried fruit you can buy at the store (e.g., raisins, pineapples, figs, dates, etc.) Dried fruits date back thousands of years B.C.
a. Why is this such an effective method of preserving food? Suggest several possibilities.
b. Fruit is often dried by being placed outside in the open under the sun in conditions that are not exactly sanitized. Why is this practice generally very safe?
5. There is great concern over healthcare-associated infections.
a. Why are healthcare settings such a âgoodâ place to catch infectious diseases? List several reasons.
b. What are several effective approaches that healthcare settings can take to minimize the spread of infectious disease?
6. Flying on an airplane includes lots of individuals in close quarters for potentially long periods of time.
a. What technology do you think airplanes use to reduce the amount of microbes from the air?
b. Despite this control method, there have been a number of documented cases of individuals infected with tuberculosis infecting other passengers during a flight. Explain how you think this happened. Which patients are at highest risk for infection, and what does this tell you about the effectiveness of microbial control on an airplane?
7. The thermal death time for a suspension of Bacillus subtilis endospores is 20 minutes in dry heat and less than 10 minutes in an autoclave. Which type of heat is more effective? Why?
8. A large hospital washes burn patients in a stainless steel tub. After each patient, the tub is cleaned with a quat. It was noticed that 14 of 20 burn patients acquired Pseudomonas infections
after being bathed. Provide an explanation for this high rate of infection.
9. If youâre on a municipal water supply, the water coming out of your faucet is chlorinated at the water treatment plant.
a. Is the water coming out of your faucet sterile?
b. Does the water still contain chlorine?
c. What are advantages and disadvantages of chlorine compared with other approaches (e.g., UV treatment, treatment with ozone).
10. You are a member of Engineers Without Borders, and your local chapter has been asked by a rural village in Thailand to assist them with improving their water supply, which they suspect of making villagers sick. The village has piping infrastructure that delivers water through a series of pipes to each household. Upon your initial site assessment of the village, you and your team determine that the water has high turbidity (particulate material) as well as a high bacterial count.
a. Design a strategy for treating the water to make it safe to drink that still relies upon the distribution system. Note that you may make some reasonable assumptions about conditions in the village (e.g., availability of electricity if you wish).
b. Identify some possible limitations of your approach.
11. A low technology approach to treating water in rural locations is to fill clear plastic soda bottles with water and leave it out all day in the sun (e.g., up on a roof).
a. What two factors are most likely at work in controlling microbes in these conditions?
b. What impact does each factor have on the microbes? Be specific.
