Assignment Task:

Task:

Learning Outcomes At the end of this laboratory assignment, students are expected to be able to:

• Plot a growth curve of the data provided on a semi-logarithmic scale

• Identify and describe the different phases of microbial growth (lag, exponential, stationary, decline)

• Calculate the growth rate and generation time from a growth curve

Background

The population of microorganisms grown in a closed system or in a batch culture (for e.g. in a test tube) often exhibits a predictable growth curve. First the cells undergo a lag phase where they adjust to the new medium, after which they start dividing constantly through binary fission in the exponential or log phase. The cells stop dividing when their growth becomes limited by different factors in the stationary phase, and eventually they lose viability over time in the death phase.

This growth curve is plotted using the number of viable cells (y axis) over time (x axis). For bacteria with short generation times as is for common laboratory organisms, time measurements are in hours. Generation times (G) can then be calculated during the exponential or log phase of growth (Refer to Lec 13:Microbial Growth I) using the formula below: ? = ? 3.3 log ?/?

Knowing the generation time and growth curve dynamic enables researchers to plan for other experiments or for other applications using the microorganism. This includes amounts to inoculate known numbers of the microorganism isolate to increase production of the microorganism; to produce antibiotics, or other products of interest; and/or to explain response of the microorganism to different antimicrobial agents. While it is possible to use published standard curves for a particular microorganism, especially if the isolate was commercially obtained; it is good practice to construct your own growth curve for the microorganism before doing other experiments as microbial growth is influenced by growth conditions that may vary from laboratory to laboratory.

 

Answer the following questions when writing your Results:

1. What is the average/mean and standard error for plate count for each day for control and experimental conditions? Which day has the lowest and highest standard error?

2. How does the log CFU/ml change over time for control and experimental conditions?

3. Are you able to identify the lag, log, stationary and death phase in using these growth curves? Are you able to calculate the generation time for this black yeast under the two conditions? Answer the following questions when writing your

Discussion: 1. What are you able to conclude about the effect of culture conditions on growth curve of Exophiala dermatitidis? How did the experimental condition affect the generation time compared to the control condition? Are these results expected? Why or why not?

2. What are some limitations in the data or the experimental procedures used to determine the growth dynamics? For example, how would missing data affect the results? How would the method used for the plate count in this experiment compare with a different method?

3. Note that the optical density (OD) is measured in the preculture protocol (Part A), but it was not measured for the experimental condition in growth assessment (Part B). What are the challenges in measuring OD for the experimental condition (PartB)?

 

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  • Uploaded By : Pearl
  • Posted on : January 02nd, 2019

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