Microbiology

Question 1

What are the 3 shapes of bacteria

Answer 1

Bacillus (Rod) - Coccus (Sphere) - Spirillum (Spiral)

Question 2

Obligate aerobes

Answer 2

bacteria that require oxygen to metabolise and carry out cell division

Question 3

Obligate anaerobes

Answer 3

bacteria that can only metabolise and carry out cell division in the absence of oxygen

Question 4

Facultative anaerobes

Answer 4

bacteria that can metabolise and divide faster with oxygen present however can grow and divide in the absence of oxygen

Question 5

What is the purpose of aseptic technique?

Answer 5

• prevent contamination of the environment
• prevent contamination of microbial cultures by unwanted microbes from the environment

Question 6

Why is all glassware Autoclaved at 121 for 15 minutes?

Answer 6

• to kill any bacteria or spores

Question 7

Why are petri dish lids opened at a small angle?

Answer 7

• prevent bacteria from entering the petri dish

Question 8

Why is a roaring blue flame on the bench?

Answer 8

• to create a convection current to uplift air away from the culture

Question 9

Keeping caps in hand and flaming the neck of the bottle

Answer 9

• to not contaminate the desk or the contents of the bottel

Question 10

flaming loops until red hot and glass spreaders using ethanol

Answer 10

kill bacteria

Question 11

in a tube culture experiment where will the types of bacteria be found

Answer 11

• obligate aerobes near the top to absorb maximum oxygen
• facultative anaerobes slightly more near top as divide better in presence of oxygen however found throughout tube
• obligate anaerobes near the bottom of the tube to avoid oxygen

Question 12

What is a Haemocyometer used for

Answer 12

to measure total cell count

Question 13

What are the advantages and disadvantages of a viable cell count

Answer 13

Advantages
- counts living cells

Disadvantages
- it is possible to underestimate the population as you cannot be sure each colony has grown from a single bacteria
- takes a long time 24+ hours for bacteria to form colonies
- if a culture is a mix of bacteria with different division rates

Question 14

What are the advantages and disadvantages of a total cell count

Answer 14

Advantages
- fast (takes only a few minutes)
- can count different cells at the same time

Disadvantages
- difficult to count clumps
- doesn’t discriminate between live or dead cells
- can be difficult to see

Question 15

What are gram positive bacteria?

Answer 15

have a thick peptidoglycan layer which retains the crystal violet stain (appears purple

Question 16

What are gram negative bacteria

Answer 16

have a thin peptidoglycan layer and a liposaccharide layer - alcohol will wash crystal violet out counter safranin will stain the cell red

Question 17

Describe the 5 steps of Gram staining

Answer 17

• heat fix a smear of bacteria
• stain using crystal violet
• fix with iodine
• decolourise with alcohol
• safranin counter-stain

Question 18

When culturing bacteria what should be present in the nutrient broth or agar

Answer 18

• carbon source, nitrogen source, water source vitamins and mineral salts
• optimum pH and temperature

Question 19

Describe how to carry out a serial dilution

Answer 19

• use a graduated pipette to transfer 0.1 cm3 into a crew cap bottle along with 9.9 distilled water 10-2
• use a graduated pipette to transfer 0.1cm3 of into screw cap bottle along with 9.9 cm3 distilled water 10-4
• repeat until 10-6
• swirl each bottle to mix gently

Question 20

How many colonies need to be present to make your selected plates representative

Answer 20

• too few colonies results in inaccurate representation
• too many results inaccuracy with counting