Lab practicals

Question 1

What are the two methods for aspetic technique?

Answer 1

Streak plate, Serial Dilution

Question 2

How do you carry out the streak plate practical?

Answer 2

1. Vortex mixer- mix culture with this
2. using metal loop at angle, in bunsen flame until glows orange
   and allow to cool for few seconds
3. Remove lid from culture bottle, pass bottle neck through flame
4. Take a loopful of culture, lightly streak quarter on agar surface
5. Flame/quench loop, turn plate and streak across from initial inoccupation
6. Repeat 3x all together, sterilise loop each time and afterwards.

Question 3

How do you carry out serial dilution?

Question 4

What is the general purpose of selective media evaluation?

Answer 4

Performing microbial counts.

Question 5

What is the difference between differential and selective media, give an example of each?

Answer 5

Differential media is used for the detection of microorganisms and by molecular biologists to detect recombinant strains of bacteria. Examples of differential media include: Blood agar.

Selective media is used to select for the growth of a particular “selected” microorganism. For example, if a certain microbe is resistant to aparticular antibiotic (e.g., novobiocin

Question 6

What is the concentration of bacteriological agar normally used in making solid media?

Answer 6

1-2% for solidifying culture media

Question 7

Why should bottle caps be loosened slightly prior to autoclaving?

Answer 7

to prevent bottles exploding

Question 8

Explain how you would examine a gram stain slide under a compound microscope?

Answer 8

Place the slide on the stage of the microscope and begin to look for stained material using a 40X objective.

Question 9

Why is the coarse focus not used once the oil immersion objective is in place?

Answer 9

may result in crashing the lens into the slide

Question 10

What is the total magnification used for the gram stain?

Answer 10

1000× magnification using a light microscope

Question 11

Name the 4 categories of organisms that can be identified by a gram stain?

Answer 11

bacteria, fungi, algae, and protozoa;

Question 12

Why must the slide be passed through a flame before staining?

Answer 12

to kill the bacteria and cause them to adhere

Question 13

Why is it important to keep pipettes upright when use?

Answer 13

To avoid contamination

Question 14

Why is it necessary to touch the loop onto the sterile agar after flaming?

Answer 14

To cool it down and prevent killing the bacteria

Question 15

Why are agar plates kept inverted whenever possible?

Answer 15

To avoid condensation dropping

Question 16

What is the purpose of serial dilution?

Answer 16

To estimate and count bacteria through diluting the sample using a known factor to calculate

Question 17

What is the purpose of a streak plate?

Answer 17

To get isolated colonies

Question 18

What are some of the reasons for not getting isolated colonies from a streak plate?

Answer 18

1. Not spread properly
2. Not sterilizing loop inbetween each streak
3. Transferring colonies

Question 19

How should molten agar be stored and why?

Answer 19

Store plates upside down in a refrigerator or cold room.

Most bacteria cannot grow well in cold temperatures.

Question 20

What are the advantages of using agar agar as a gelling agent?

Answer 20

high gel strength at low concentrations, it is stable over a wide range of temperatures

Question 21

Under which circumstances would you use enrichment media, with example?

Answer 21

when high sensitivity is required e.g. for detection of bacteria from CSF, or to detect small numbers of Salmonella