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coffeespider648Lv1

28 Sep 2019

Cytokines, Chemokines, and Their Receptorsâ

-Note several ways that cytokines regulate the immune response,

-emphasis on mechanisms to slow down or limit the immune response.

-In your answer, discuss why you think these control features are important and describe a potential therapeutic application of one of the control mechanisms, including possible applications of this potential therapeutic treatment.

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Casey DurganLv2

28 Sep 2019

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13. Describe the four mechanisms by which bacteria can become resistant to antibacterial drugs. Describe two ways bacteria may be genetically modified to achieve drug resistance naturally.

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.

amberraven287

yeast population dynamics

Procedure

1. Work in pairs on this lab, so 12 tubes per pair of students. And share a tube rack with one other pair of students

2. Turn on your spectrophotometer. It needs at least 15 minutes to warm up to give you good readings.

3. Add 5 mL of yeast extract solution (YECM) to each of 12 tubes. (The yeast extract provides vitamins and amino acids for yeast growth and will be the same for all cultures). The tubes should be labeled with your initials, treatment, and tube number. Tape or Parafilm down the lids of 3 tubes, and label them âCONTROLâ.

Do not touch the insides of the tubes or lids! Try to keep these as sterile as possible!!

4. Add 50 mL live yeast culture to each of the remaining 9 tubes.

5. Add the varying volumes of sugar and/or ethanol using Table 1 below.

6. Use Parafilm to close the tops of each tube, making sure the Parafilm is tight and no air can get in, and label each tube with the following:

Amount of sugar added (mL) Amount of ethanol added (mL)

Name of your group Tube number

Table 1: setup yeast tubes (remember, 1 mL = 1000 mL)
Tube number	Yeast culture medium? (5 mL)	Live yeast culture? (50 mL)	Sugar added (mL)	Ethanol added (mL)
1 â control	YES	NO	0	0
2 â control	YES	NO	0	0
3 - control	YES	NO	0	0
4	YES	YES	0	0
5	YES	YES	0.25	0
6	YES	YES	0.5	0
7	YES	YES	0	0.25
8	YES	YES	0.25	0.25
9	YES	YES	0.5	0.25
10	YES	YES	0	0.5
11	YES	YES	0.25	0.5
12	YES	YES	0.5	0.5

Procedure for measuring absorbance (in absorbance units, or AU)

7. Calibrate the spectrophotometer:

Turn on the spectrophotometer and let it warm up for 15 minutes. You will get erroneous results if you donât let it warm up first.

Be sure the spectrophotometer is set to read at the wavelength of 550 nm

With no tube in the spectrophotometer and the lid closed, use the left-hand knob to adjust the reading to 0% Transmittance/push zero button to calibrate

Insert a CONTROL tube (making sure it is clear, without bacterial contamination which would make it cloudy), and use the right-hand knob to readjust the spectrophotometer to 100% Transmittance.

When reading the absorbance, be sure to line up the needle on the spec with its reflection.

8. Immediately before reading any tube, vortex the tube so that the spinning column reaches the bottom of the tube for several seconds. This is critical! The yeast cells are heavy and will tend to sink to the bottom of the tube, so you must vortex the tubes to resuspend them: otherwise, your spectrophotometer readings will be erroneously low. If the vortex is not enough to suspend the pellet of yeast cells at the base of the tube, take a piece of Parafilm and cover the top of the tube, then cover this with your thumb and shake the tube vigorously. The pellet should dislodge and the yeast cells should be easily resuspended after doing this. Use a Kimwipe to wipe down the outside of each tube, to remove fingerprints and other smudges that could affect the absorbance reading. (COULD BE A POTENTIAL ERROR)

9. Record the absorbance (in absorbance units, AU) for the tube on your data sheet.

10. Repeat steps 5 and 6 for every tube.

11. Leave the spectrophotometer turned on for the next user.

Figures you should include are:

Average absorbance vs. time for the no ethanol (0 mL) treatment

Average absorbance vs. time for the 0.25 mL ethanol treatment

Average absorbance vs. time for the 0.50 mL ethanol treatment

Sugar added vs. average carrying capacity (K). Use different symbols to denote each of the three alcohol concentrations

A. After a limit, the increasing concentration of sugar decreases the carrying capacity and growth rate. This is because at higher sugar concentrations, the medium becomes hypertonic and the yeast cells loss water towards the medium.With increasing concentration of the ethanol, the carrying capacity and the growth rate decreases. Why does this happen?

B. Is there any interaction between the effects of adding sugar and alcohol on yeast?

C. why do some cultures not reach K?

D. What are the potential sources of error and assumptions made in this experiment?

E. What do these results mean in a more general (non-yeast) context?