Quiz 4

Question 1

What is a unique characteristic about viruses?

Answer 1

viruses are obligate intracellular

they need to live in a host to replicate

Question 2

What is a bacteriophage? give an example from lab

Answer 2

• a bacteriophage: a virus that infects a bacteria

- an example is T4

Question 3

What is the diff between doing an assay for a virus vs a bacterium? what do u count?

Answer 3

• for a virus: plaques are counted or clear ones

- for a bacteria: colonies of cells are counted

Question 4

What are the units for a viral assay?

Answer 4

PFU: plaque forming units

Question 5

What are the bacteria that are commonly found in yogurt?

Answer 5

Streptococcus thermophilus

Lactobacillus bulgarius

Question 6

What is the main organism in yeast, and what causes bread to rise in yeast?

Answer 6

• Sacchromyes cervisae

- CO2 causes bread to rise in yeast

Question 7

Define indicator organism and give an example

Answer 7

• an organism that indicates contamination

ex. coliform

Question 8

lytic v lysogenic

Answer 8

• lytic: results in cell lysis

- lysogenic: viral DNA is integrated into bacterial DNA

Question 9

How do you count a viral assay

Answer 9

-count all the clear zones and put it in scientific notiation
if you count 32, multiply it by dilution (10^-6) -> 3.2x10^7

Question 10

What is the gray area of a viral assay? What do the clear cells mean?

Answer 10

• gray: non lysed cells

- clear: plaques = viral count = lysed cells

Question 11

The organism responsible for food poisoning and food intoxications are always apparent in food products as they severely alter the taste and odor of food

Answer 11

FALSE

Question 12

Viruses can infect which of the following:

Answer 12

answer: all of the above
- bacteria
- animals
- plants

Question 13

Why was there a 10 minute incubation period before plating onto the bottom agar?

Answer 13

this gives the T4 time to infect and attach to the host which was E. coli .