Question

33. In the quadrant streak plate method for producing isolated colonies, how many times should your inoculating loop enter the test tube of liquid bacterial culture (from which you are obtaining cells)?

1. 1
2. 2
3. 3
4. 4
5. None of the above

34. In the quadrant streak plate method for producing isolated colonies, which quadrant should yield the best developed (e.g. full size, good separation from other colonies) isolated colonies, when the method is performed correctly?

1. First
2. Second
3. Third
4. Fourth
5. Fifth

35. From the list of plates below, each with a different number of colony forming units (CFUs), which one is most appropriate for calculating CFU/ml?

1. 1
2. 10
3. 100
4. 500
5. 1,000

36. You plated 1 ml from a 10^-4 dilution of E. coli and a plate with 230 CFU resulted.  What is the number of CFU/ml?

1. 2.3x10⁴
2. 2.3x10⁵
3. 2.3x10⁶
4. 2.3x10⁷
5. 2.3x10⁸

Answer 1

33) Option a: 1

The inoculating loop nmust eter the test tube of liquid bacterial culture only once. This will be the starting point of the streaking process. The amount of bacteria will then gradually dilute as we progress with streaking.

34) Option d: Fourth

In the quadrant streak plate method. the bacterial culture picked up in the inoculation loop is diluted gradually, as by the time it reaches the fourth quadrant, only a few cell are deposited in the streak lines. Thus, the fourth quadrant yields the best colonies.

35) Option c: 100

The ideal range for counting colonies to identify CFU/ml is between 30 and 350 colonies. Less tha 30 is "Too Few To Count" and more than 350 is "Too Numerous To Count"

36) Option c: 2.3x106

CFU/ml is calculated as the number of colonies multiplied the reciprocal of the fold dilution factor.. Thus here it will be 230 x 104  = 2.3x106