Microbiology: Principles and Explorations
9th Edition
ISBN: 9781118743164
Author: Jacquelyn G. Black, Laura J. Black
Publisher: WILEY
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Chapter 6, Problem 21SQ
Summary Introduction
Introduction: Plate count techniques are mainly based on bacterial cell reproduction on the agar plates. It is a traditional method, and it is used for probiotic product quality assurance.
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A sample of Earth Alive Soil Activator was diluted by transferring 1 gram into a 9 ml dilution blank (tube A) and then serially diluted five (5) more times by transferring 1 ml of a previous dilution into a tube of 9 ml of sterile water. After making these serial dilutions, 2 ml samples were taken from tubes D, E, and F, added into empty petri dishes, and molten PCA was poured into each petri dish. Tubes A, B, and C were heated in a 80˚C water bath for 30 minutes, 2 ml samples of these tubes were added into empty petri dishes, and molten PCA was poured into each petri dish. These plates were allowed to solidify, and they were incubated at 35˚C for 48 hours. After the incubation period, you counted CFUs on all 6 plates. The results of your CFU counts are contained in table 1.
Table 1. CFU counts for 3 plates from the heated dilutions (A-C) and the 3 plates from the non-heated dilutions (D-F)
# CFUs
Not heated
Heated
A
--
400
B
--
45
C
--
6
D
350
--
E
31
--
F
2
--…
In this experiment, a culture was serially diluted to the concentrations below. Each plate was plated with 0.25mL of the dilution. Using the most diluted plate, what is the correct concentration of the original culture?
A) 2.0 X 10^-3 cells/mL
B) 2.0 X 10^5 cells/mL
C) 4.0 X 10^5 cells/mL
D) 5.0 X 10^4 cells/mL
A culture is incubated for 10 hours.
1 hours after inoculation it reached
the exponential growth phase. At
this time point the cell density was
1x10^4 cells/ml. 5 hours after
inoculation (still during the
exponential growth phase) the cell
density was 1x10^7 cells. Calculate
K and g(t).
The growth constant (k) is
minute. (round to 3 decimal points)
The generation time (gt) is
minutes. (round to whole number)
Chapter 6 Solutions
Microbiology: Principles and Explorations
Ch. 6 - What are the differences between the lag phase and...Ch. 6 - How does logarithmic rate of increase differ from...Ch. 6 - Prob. 1.3SCCh. 6 - Why does a direct microscopic count of bacteria...Ch. 6 - What does the ending -phile mean? Distinguish...Ch. 6 - What enzymes do most obligate anaerobes lack? How...Ch. 6 - Prob. 2.3SCCh. 6 - Prob. 3.1SCCh. 6 - Distinguish between the various kinds of media:...Ch. 6 - What is the purpose of a stock culture? Why is it...
Ch. 6 - Prob. 1CCSCh. 6 - Exactly 100 bacteria with a generation time of 30...Ch. 6 - In the above example, do you think that the number...Ch. 6 - Prob. 3CTQCh. 6 - Prob. 1SQCh. 6 - Match the following growth phase terms to their...Ch. 6 - Which of the following is the best definition of...Ch. 6 - Prob. 4SQCh. 6 - The most probable number (MPN) technique is a...Ch. 6 - Match the terms with their definitions:Ch. 6 - Prob. 7SQCh. 6 - Why do foods containing a high concentration of...Ch. 6 - Some bacteria have complex nutritional...Ch. 6 - Prob. 10SQCh. 6 - Which type of cell will shift to aerobic...Ch. 6 - Which of the following statements about endospores...Ch. 6 - Prob. 13SQCh. 6 - Blood agar is often used to observe changes in the...Ch. 6 - A bacterial medium that contains 20 grams of beef...Ch. 6 - MacConkey agar contains the dye, crystal violet,...Ch. 6 - Prob. 17SQCh. 6 - What are the purposes of carrying out the streak...Ch. 6 - Prob. 19SQCh. 6 - During quorum sensing, bacteria sense their...Ch. 6 - Prob. 21SQCh. 6 - Identify the position of each of the following on...
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- As shown in this diagram, you perform a ten-fold serial dilution of a culture to determine the number of colony forming units (CFU) per mL it contains. You do a plate count with these growth results (no. of colonies for each dilution): 1:10 too many to count; 1:100 too many to count; 1:1,000 174; 1:10,000 23; 1:100,000 no growth. The number of CFU per mL in the original culture was: 1 ml 1 ml Original inoculum Dilutions 9 ml broth in each tube 1:10 1 ml 174,000 1:100 1 ml 1 ml 1 ml 1:1000 1 ml 1:10,000 1 ml None of the other four answers (Correct answer not given) 1,000 230,000 174 1 ml 1:100,000 1 mlarrow_forward(1) why can't we say "sterile" technique (2) how are aseptic technique similar and different in the lab and Healthcare field?Be specific and explain at least 2 differences and two similarities. (3) You are asked to develop a method of transfer an unknown organism from a liquid broth to a solid petri dish.list each step that you would have to take .be specificarrow_forwardAndrew has to prepare 30 plates (use maximum volume), 15 slants (small test tube), and 15 stabs (big test tube) of Luria Bertani Agar. a. What is the total volume of the medium needed? b. What is the amount of each component needed, given the following media composition per liter of distilled water:arrow_forward
- For the juice samples in exercise 3-4, you will be using the pour plate technique. In this exercise, you will add juice to a petri dish and pour agar over the sample and mix. Why is the media (potato dextrose agar, PDA) kept in a water bath until you are ready to use it, and why must you work fairly quickly? (One response answers both questions). The media is already solid and will form chunks The media has a dye added to it that must be kept at 45°C until ready to use O PDA is a media that allows growth of many types of fungi, and the heat from the water bath keeps the fungal spores from growing. The media is kept liquid in the water bath with heat, removing the tube from the heat source will cause the PDA to solidifyarrow_forwardBlood agar is often used to observe changes in the appear-ance of the agar around the colonies growing on this medium.This medium could then be called:(a) Selective(b) Designated(c) Differential(d) Defined(e) Exactarrow_forwardWhat are the expected problems in the centrifuge in case of imbalance of samples ? *arrow_forward
- After incubating for 24-48 hours, you retrieve your 4 agar plates for the osmotic pressure exercise from the 37°C incubator. You observe the following results: • Sa = Staphylococcus aureus • Pv = Proteus vulgaris Sa For each organism, you should indicate in the text box below: 1. At what salt concentrations (osmotic pressures) you saw growth. 2. The classification term you would use in order to classify the organism based on osmotic pressure. Choose your term based upon where you observed growth; not optimal growth. Each organism has only one classification term associated in describing its growth pattern(s). You will need to use the osmotic pressure classification descriptions and terms outlined in your lab manual.arrow_forwardFive grams of soil were added to 45 ml of sterile water and shaken vigorously. After that, 0.1 ml of this was added to 9.9 ml of sterile water. This was further diluted by four successive 1/10 dilutions. The last dilution was used to prepare a spread plate. After incubation, 58 colonies were present on this plate. What is the CFU/g of the soil sample? Assume: 1 g = 1 mLarrow_forwardHow do you calculate the initial concentration of a sample? How would you make a 1:10 dilution of a broth culture if the final volume of the dilution is 10 ml? How much broth, and how much diluent, would you add? If you made a series of tenfold dilutions, exactly the same way as you described in question 1, what would be the dilution factor in the fifth tube? The following are errors that people commonly make when they perform serial dilutions. Indicate whether you think that the number of cfu/ ml calculated would be too high or too low if you make this mistake. You intend to add 0.9 ml of diluent to each tube and 0.1 ml of culture. Instead, you add 0.5 ml of diluent to each tube and 0.1 ml of culture to the first tube. Then, you make a serial dilution of 0.1 ml into and from each tube as described. You prepare 0.9 ml of diluents in each tube. You add 0.1 ml of culture (from the overnight culture provided) to every tube. You add 0.9 ml of diluent to each tube. You add 0.1 ml of…arrow_forward
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