Homework chapter 22 - 25 (Due April 17th)

(Yoli) page 182 Question 1 - 4
It's done!



(Indy) Page191 question 1 

Distinguish between respiration and fermentation

In Fermentation an organic substrate serves as the final acceptor; whereas in respiration, either inorganic ion are (anaerobic) or oxygen is the final electron acceptor (aerobic).

(Indy) page 192 question 2 and 3   

2) Do all microorganisms use pyruvic acid in the same way? Explain

No, they do not. Metabolism of pyruvate is not the same for all microorganisms. A variety of end products results define their different fermentative capabilities

3)Describe a pathway used for the degradation of carbohydrates by strict anaerobes
Anaerobic organisms break down carbohydrates using the pentose-phosphate pathway. Glycolysis is used by aerobic and anaerobic organisms in energy production.

(Yaneli) page 192 question 4 and  5





4. From your experiment data, you know that P. aeruginosa did not utilize any of the carbohydrates in the test media. In this view of this how do these organisms generate energy to sustain their viability?
It may be using acetate, which is not a carbohydrate and ammonium, or some other simple organic compounds that are present in the agar, without needing to utilize the more complex carbohydrates in the test media. Regardless, it utilizes these compounds via aerobic metabolism and that is how it generates the energy it needs to sustain their viability.

5. Clostridium perfringers, an obligate anaerobe, is capable of utilizing the carbohydrates released from injured tissues as an energy source. During the infectious process, large amounts of gas accumulate in the infected tissues. Would you expect this gas to be CO2? Explain.
Probably not expect carbon dioxide to be produced as a consequence of carbohydrate fermentation, but in reality, this does occur because Clostridium has a varied fermentation pathway, some of which produces carbon dioxide.

(Yanel) page 201 question 1 
1. Explain the function of the 0.1% agar in the nitrate medium.
It makes the media semi solid, which selects the organisms that are anaerobic, which is required for nitrate reduction.

(Lupe) page 202 question 2 – 5

2. Explain the functions of Solutions A and B

they show whether nitrate reduction occurred by turning red. If no color change then nitrate has remained the same.

3. If a culture does not undergo a color change on the addition of Solutions A and B, explain how you would interpret this results.

1- Nitrates were not reduced

2- Nitrates were reduced beyond the nitrite stage to ammonia or molecular nitrogen

4. Explain why the development of a red color on the addition of zinc is a negative test

Since zinc reduces nitrates to nitrites, a pink or red color will appear and verifies the fact that nitrates were not reduced to nitrites by the bacteria (a negative test).

5. Discuss the relationship between an organism’s ability to reduce nitrate past the nitrite stage and the organism’s proteolytic acitibity.

It means that the bacteria had such an active nitrate reductase it reduced the nitrate to ammonia and molecular nitrogen gas. As a result it has a very fast metabolism for nitrate.

Janelly's work (page 152, questions 1-6)

1. Compare the heat sensitivity of fungal spores to that of bacterial endospores.

• Fungal spores are more sensitive to heat than bacterial endospores. For example, fungal spores can be killed at 60 C. However, the endospores of bacillus can stand 100 C. It takes 121 C in the autoclave to sterilize things.  

2. Compare the effectiveness of autoclaving and dry heat.

• Sterilization in an autoclave is most effective when the organisms are either contacted by the steam directly or are contained in a small volume of aqueous (primarily water) liquid. Under these conditions, steam at a pressure about 15 psi; attaining temperature (121oC) will kill all organisms and their endospores in about 15 minutes.
• Dry heat sterilization can be an effective method of sterilization, using gravity or mechanical convection ovens. Dry heat can also sterilize items that can not be sterilized in steam or chemical sterilizers, such as powders and oils, or those that are prone to rust. In addition, Dry heat can be used for glassware, as it will not score or erode the surface as, steam might do, and dry heat will not corrode or rust instruments or needles.

3. Give an example of an application (use) of thermal death time.

• In order to make sure our food is sterile enough to eat, we must know the thermal death time of whatever type of microbes might be living in it. An example is, when food canning is taking place.

4. In the exercise, was the thermal death time or thermal death point determined?

5. Give an example of a nonlaboratory use of each of the following methods to control microbial growth:

• a. Incineration: cremation of the dead
• b. Pasteurization: milk
• c. Autoclaving: metals to be inserted into surgical tools and equipment

6. Define pasteurization. What is the purpose of pasteurization?

• Pasteurization is a process of heating food, which is usually a liquid, to a specific temperature for a predefined length of time and then immediately cooling it after it is removed from the heat
• Its purpose is to reduce the bacterial population of a liquid such as milk and to destroy organisms that may cause spoilage and human disease.

Lupe's Work for March 12,2014

Critical Thinking

1.       Explain why fungi and Bacillus sometimes grow better after heat treatment.

Fungi and Bacillus are producing endospores. Heat activates these endospores meaning the bacillus and the fungi are able to divide and replicate because the heat has activated the endospores. 

2.       The decimal reduction time (DRT) value is the time it takes to kill 90% of cells present. Assume that a DRT value for autoclaving a culture is 1.5 minutes. How long would it take to kill all the cells if 10^6 cells were present? What would happen if you topped the heating process after 9 minutes?

It will take1.5 minutes to kill 90% of the cells. Therefore, after 1.5 minutes, 10% remain. After three minutes, 1% remain. So, to figure out how long it would take to kill a million cells, you repeatedly multiply 10^6 by 0.1 until your answer is less than 1. So: 

10^6 x (0.1)^7 = 0.1 

Therefore, you need 10.5 minutes of killing to kill one million cells. 7 x 1.5 minutes = 10.5 minutes. 

After 9 minutes you would have: 

10^6 x (0.1)^4 = 100 cells left

3.       Indicators are used in autoclaving to ensure that sterilization is complete. One type of chemical indicator turns color when it has reached a specific temperature; the other type turns when it has reached a specific temperature and been exposed to steam. Which type of indicator should be used?

Tape indicators will change color when the temperature hits over 120. This indicates that the  required temperature was attained and you are unlikely to have heat-resistant spores around. This is the best indicators to be used.

4.       A biological indicator used in autoclaving is a vial containing 10^9 Bacillus stearothermophilus cells that is placed in the autoclave with the material to be sterilized. After autoclaving, the vial is incubated and examined for growth. Why is this species used as opposed to E. coli or B. subtilis?

The substance is used because it can withstand high temperatures which are needed to be sterilized without the bacteria dying. It is a thermophilic which has the presence of heat-resistant endospores.