Laboratory assignment

The following questions are from two exercises (dilutions/pipetting and counting bacteria) that you read/studied. As reference materials, read lab manual, lab exercise PPts and/or study guides and answer questions given below fully/completely in the spaces provided as instructed. Please submit assignment before or on the due date. Hand written answers are not acceptable, except calculations.

You may submit assignment as an attachment to an email. Alternatively, you may scan assignment or take a photo it and submit as an attachment to an email.

Part One: Pipetting and Dilutions

A. 1. Objectives of this exercise – briefly describe the objectives of this exercise in your own English (refer to lab manual or PPt)

A. 2. Define Solute:

A. 3. Define Solvent:

A. 4. Define dilution:

A. 5. Define solution:

B: Pipetting and Dilutions

B. 1. For each set of dilutions in figure below, calculate the amount of colored substance (dilutions) in the last test tube of each set. Show calculation steps and results in the spaces provided.

B. 2. For questions B. 2. 1—B. 2. 3 in lab manual, first write down each question and then give the corresponding answers.

B. 2.1. What is the “meniscus”?

B. 2. 2. If you transfer 0.1ml of a sample into a 99.9ml saline blank, what is the dilution factor (show calculation steps)?

B. 2. 3. How much fluid is IN the pipette below? _________________________.

B. 3. For the following 3 questions (B. 3. 1 – B. 3. 3) in lab manual, first determine:

· The number of countable colonies (colony forming units, CFUs) that fall within the range of 30-300.

· The dilution factor that gave the count (example: 10-4 or 1/104)

· The amount of diluted sample plated/added (in ml) to each plate that gave the corresponding count.

· Then calculate the number of bacteria in 1 ml of original (undiluted) sample (solid or liquid) using formula given in manual or PPt. Show calculation steps.

Note: If sample is solid (example: hamburger meat), report count as CFUs per gram of meat. If sample is liquid (example: milk), report count as CFUs per ml of milk.

B. 3. 1.

B. 3. 2.

B. 3. 3.

Part two: Counting (enumeration) bacteria

2. 1. Objectives of this exercise – briefly describe the objectives in your own English (see lab manual)

2. 2. What is viable plate count?

2. 3. What do you use to determine the number of bacteria in suspension by the turbidimetric method?

2. 4. For questions 2. 4. 1 — 2. 4. 6 in lab manual, first write down each question and then give the corresponding answers.

2. 4. 1. Data collection (Insert data table here from PPt)

2. 4. 2. Why do you have to do a standard plate count when running turbidity values the first time?

2. 4. 3. If you have a graph for E. coli, can the same graph also be used for another bacterium, like Staph?

2. 4. 4. How is “transmission” different from “absorbance”?

2. 4. 5. Give the formula for calculating the number of bacteria in 1 ml or 1 gram original sample (example: cheese or fruit juice). (Show calculation steps.

2. 4. 6. Using the formula in above question, calculate the bacterial count per milliliter of E. coli suspension in the original culture tube.

Important: To complete data table (2. 4. 1), enter count (2. 4. 6, above) into y-axis column (first for original E. coli) in data table (question # 2. 4.1.) given in PPt. Then divide count by 2 (or multiply count by ½) to enter count for each corresponding absorbance value under x-axis column. Finally enter zero (0) for both x- and y-axis columns.

2. 4. 7. Finally, using Excel graphic software, plot a standard curve using data from step 2. 4. 1, above. When entering your data in Excel graphic, start with the zero values (X-axis=0 and Y-axis=0) and finish with the highest values. Use absorbance column values for X-axis and the number of E. coli calculated for Y-axis. To plot the graph, follow the steps given in your manual. Please include curve/graph with the rest of report and submit before or due date. Be warned that no assignment is accepted after due date.

Due date: Friday, June 19 @midnight

 

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