Midterm_Pure Culture Technique

Question 1

contains only a single kind of an organism

Answer 1

pure cultures

Question 2

contains more than one
kind of organism

Answer 2

mixed culture

Question 3

methods for obtaining pure cultures

Answer 3

streak plate
pour plate

Note:
- Both procedures involve diluting the bacterial cells in
a sample to an end point where a single cell divides,
giving rise to a single pure colony

Question 4

• procedure most often
  used by microbiologists to obtain pure cultures.
• simple and allows for economy of materials
• requires a certain level of skill which is only obtained through practice

Answer 4

streak-plate method

Question 5

Types of Streak

Answer 5

Quadrant Streak (Method A)
Quadrant Streak (Method B)
Radiant Streak

Question 6

Types of Streak

(1) Streak one loopful of organisms over Area 1 near edge of the plate. Apply the loop lightly. Don’t gouge into the medium.

(2) Flame the loop, cool 5 seconds, and make 5 or 6 streaks from Area 1 through Area 2. Momentarily touching the loop to a
sterile area of the medium before streaking insures a cool loop.

(3) Flame the loop again, cool it, and make 6 or 7 streaks from Area 2 through Area 3.

(4) Flame the loop again, and make as many streaks as possible from Area 3 through Area 4, using up the remainder of the plate surface.

(5) Flame the loop before putting it aside.

Answer 6

Quadrant Streak (Method A)

Question 7

Types of Streak

(1) Streak one loopful of organisms back and forth over Area 1, starting at point designated by “s”. Apply loop lightly. Don’t gouge into the medium.

(2) Flame the loop, cool 5 seconds, and touch the medium in a sterile area momentarily to insure coolness.

(3) Rotate dish 90 degrees while keeping the dish closed. Streak Area 2 with several back and forth strokes, hitting the original streak a few times.

(4) Flame the loop again. Rotate the dish and streak Area 3 several times, hitting the last area several times.

(5) Flame the loop, cool it, and rotate the dish 90 degrees again. Streak Area 4, contacting Area 3 several times and drag out the culture as illustrated.

(6) Flame the loop before putting it aside.

Answer 7

Quadrant Streak (Method B)

Question 8

Types of Streak

(1) Spread a loopful of organisms in a small area near the edge of the plate in Area 1. Apply the loop lightly. Don’t gouge into the medium.

(2) Flame the loop and allow it to cool for 5 seconds. Touching a sterile area will insure coolness.

(3) From the edge of Area 1 make 7 or 8 straight streaks to the opposite side of the plate.

(4) Flame the loop again, cool it sufficiently, and cross streak over the last streaks, starting near Area 1.

(5) Flame the loop before putting it in its receptacle.

Answer 8

Radiant Streak

Question 9

• method of separating one species of bacteria from another consists of diluting out one loopful of organisms with three tubes of liquefied nutrient
  agar in such a manner that one of the plates poured
  will have an optimum number of organisms to provide good isolation
• requires somewhat less skill than that required for a
  good streak plate
• requires more media, tubes, and plates

Answer 9

Pour-Plate Method