Ex. 1-5; 1-6

Question 1

Mixed culture

Answer 1

A microbial culture consisting of two or more species

Question 2

Pure culture

Answer 2

A microbial culture consisting of only a single species

Question 3

What is the first step to identifying an organism?

Answer 3

Obtaining isolation of individual species from a mixed sample

Question 4

What are two commonly used isolation techniques?

Answer 4

Streak plate and spread plate

Question 5

What is a quadrant streak generally used for?

Answer 5

For a high density sample such as a broth or slant

Question 6

What is a zig zag streak generally used for?

Answer 6

A low density sample such as a swab

Question 7

What type of plate did we use for our streaks?

Answer 7

Nutrient agar plate

Question 8

What is the goal of he streak method?

Answer 8

To isolate individual colonies from a high density culture

Question 9

Define colony as used in biology.

Answer 9

Mass of genetically identical cells

Question 10

In a quadrant streak how do you isolate the colonies? (Method)

Answer 10

The original sample is spread on the plate in quadrants, each time decreasing the density, leading to individual cells being deposited separately on the agar surface.

Question 11

What are the two bacterial samples we used for the Quadrant Streak and what was their colony morphology?

Answer 11

Micrococcus luteus - tiny circular colonies, smooth edges (margin), convex (elevation), beige to yellow (color), shiny and smooth (texture)
Staphylococcus epidermidis - small circular colonies, smooth edges (margin), convex (elevation), off-white (color), smooth (texture)

Question 12

What is the spread plate method of isolation?

Answer 12

A method in which a diluted microbial sample is deposited on an agar plate and spread uniformly across the surface with a glass rod (we used metal).

Question 13

What does CFU stand for and what does it mean?

Answer 13

Colony-forming unit -

Colony origin

Question 14

What are the sources that we used for Quadrant Streaking?

Answer 14

slant and broth

Question 15

What source did we use for the Spread Plate method?

Answer 15

broth

Question 16

What was the procedure for the spread plate?

Answer 16

1. place 15 drops of sterile water in each of 4 microfuse tubes
2. Generate a serial dilution by taking 3 drops from a stock bacterial sample and placing in tube 1. Then take 3 drops from tube 1 and place in tube 2. then take 3 drops from tube 2 and place in tube 3. Then 3 drops from tube 3 to 4.
3. Take 4 drops from tube 4 and apply to the nutrient rich agar plate
4. spread with rod evenly over the surface of the plate
5. After incubated - get estimate of the CFU (colony forming units)

Question 17

Why would you use the spread plate method?

Answer 17

You would use it in order to determine the number of CFU/mL.

Question 18

How do you determine the CFU/mL? (equation)

Answer 18

Count the number of colonies on the plate and multiple that number by the dilution factor.