Pre-Lab #3

Question 1

1. What is aseptic technique and why is it important in microbiology?

Answer 1

a. Aseptic Technique is a procedure that is used to prevent cross contamination. This is important because we want to know what colony we are looking at and not have it be contaminated

Question 2

2. What are the two instruments used to transfer bacteria?

Answer 2

a. Inoculation loop and Inoculation needle

Question 3

How do we sterilize these instruments?

Answer 3

a. Sterilize them by passing them through the hottest part of the flame

Question 4

What is the hottest part of a flame?

Answer 4

a. The tip of the cone

Question 4

When do you flame the mouth of a test tube?

Answer 4

a. Pass the mouth of the flame tube through the flame when you remove the lid and after you take your sample before placing the lid back on

Question 5

Why is it bad to touch your bacterial sample with a hot wire?

Answer 5

a. It is bad to touch your bacterial sample with a hot wire because if it is too hot you could kill your microorganisms

Question 6

What is a pure colony?

Answer 6

a. A colony grown from a single parent cell

Question 6

What is the goal of the streak plate technique?

Answer 6

a. The goal is to view isolated colonies

Question 6

List four characteristics used to describe colony morphology.

Answer 6

a. Size, shape, color texture

Question 7

Why is the loop flamed between quadrants?

Answer 7

a. Reduce the load of the organism to there is a better chance of getting isolated colonies

Question 8

How does colony morphology assist in the identification of a bacterial species?

Answer 8

a. Colony morphology assists in the identification of a bacterial species because all the species look relatively similar so the colony morphology provides visual cues

Question 9

One way we can follow bacterial growth is by determining the Colony Forming Unit (CFU) count using the spread plate technique. Why is serial dilution used in this technique to determine the CFU count?

Answer 9

a. Serial dilution is used to decrease a bacterial population to a required concentration. This helps achieve an appropriate concentration for a specific test method

Question 10

What is a colony forming unit or CFU?

Answer 10

a. A unit that is used to estimate the number of viable microbial cells in a sample

Question 10

What is the goal of the spread plate method?

Answer 10

a. To evenly distribute a liquid sample containing bacteria across the surface of an agar plate

Question 11

What is a logarithmic dilution?

Answer 11

a. A 10-fold solution which means the concentration is decreased by a multiple of 10

Question 12

Is it possible to determine the number of dead bacterial cells present in a sample using the spread plate method? Explain. (This is a reasoning question; you need to apply your understanding to come up with the answer).

Answer 12

a. No I do not think that it is possible to determine the number of dead cells in a sample. I think that this is true because only live cells will grow so if they are dead they will not grow therefore you will not be able to see to count them

Question 13

6. Is it possible to determine the number of living bacterial cells present in a sample using the spread plate method? Why or why not? (This is a reasoning question; you need to apply your understanding to come up with the answer).

Answer 13

a. Yes I do think that you would be able to count the number of living bacterial cells present in the sample because they are living so they would grow. Since they would grow you would be able to see them and then therefore determine the number.

Question 14

7. Insert the formula for CFU/mL here: (#colonies counted)X)Dilution factor)/Volume

Answer 14

a. If a 0.1 ml of a 1:106 dilution plate contains 56 colonies, calculate the number of bacterial cells per ml of the original culture.
a. 560,000,000
b. If you plate 200 ul of a 1:100,000 dilution and get 123 colonies, what is the number of CFU/mL in the original sample?
a. 61,500,00CFU/mL