LabMidterm

Question 1

Two precautions

Answer 1

• No eating/drinking
• Labcoat
• Wash hands frequently

Question 2

Phase contrast microscopy useful for viewing

Answer 2

wet mounts (unstained slides)

Question 3

When streaking agar solution… Failing to loop would result in..

Answer 3

No isolated colonies.

Question 4

Primary stain

Answer 4

Crystal violet

Gram + and Gram - are purple…

Question 5

Mordant

Answer 5

Gram’s iodine

Gram + and Gram - are purple…

Question 6

Decolourizer

Answer 6

Acetone - Alcohol
Gram + (purple)
Gram - (clear, colourless)

Question 7

Counterstain

Answer 7

Safranin
Gram + (purple)
Gram - (pink)

Question 8

What step in gram stain process makes stain differential?

Answer 8

Decolourizer - acetone-alcohol. It rapidly decolourize Gram - bacteria and gram+ will remain purple. Thin wall of negative allows the iodine to wash out easily

Question 9

Positive string test indicates..

Answer 9

Gram negative cell wall

Question 10

Antibiotics are natural chemicals.. explain

Answer 10

Antibiotics are made from microorganisms and are therefore natural.. They are not synthetic (created in a lab)

Question 11

Factors that will affect the zone of inhibition with disc with disinfectant..

Answer 11

• type of bacteria/bacterial resistance
• concentration of disinfectant in disc
• pH of disinfectant

Question 12

Physical conditions necessary for sterilization in autoclave

Answer 12

15 psi, 121degrees for 20 mins

Question 13

Method used to ensure proper operation of autoclave

Answer 13

autoclave tape or strips with heat sensitive dye used. when proper conditions reached - invisible dye becomes visible.

Question 14

Choice of sterilizing a flask of culture medium?

Answer 14

autoclaving

Question 15

choice of sterilization for plastic petri dishes?

Answer 15

gamma radiation

Question 16

Chioce of sterilization for liquid?

Answer 16

filter sterilization

Question 17

Why agar side up?

Answer 17

So nothing drips from the top onto the experiment being carried out. Ex - condensation won’t collect on agar, but on lid instead.

Question 18

Well streaked if…

Answer 18

individual colonies

Question 19

punctiform

Answer 19

small dots.. <1mm dia

Question 20

entire

Answer 20

whole margin

Question 21

undulate

Answer 21

wonky line

Question 22

filamentous

Answer 22

bundles

Question 23

bascillus

Answer 23

Bacillus is a genus of Gram-positive, rod-shaped bacteria

Question 24

String test

Answer 24

KOH added, cell walls break down if negative and dna strings behind a loop as lifted. In positive, cell walls fail to break down in KOH

Question 25

structural stains

Answer 25

used to identify specific parts of microorganisms. Help to identify spores or capsules etc

Question 26

Capsules

Answer 26

slimy gelatinous layer of material surroundings bacterial cell.

• can’t be stained. Halo effect
• not heat fixed prior to staining because capsule would be affected and results inconclusive

Question 27

four ways to adjusting illumination on light microscope

Answer 27

• condenser diaphragm
• condenser
• light intensity adjustment
• phase contrast microscopy option

Question 28

peptidoglycan

Answer 28

structure in cell walls

Question 29

boiling

Answer 29

does not kill endospores