Question

A microbiologist streaked a mixed culture of three different bacterial species across 4 different quadrants of a nutrient agar plate. Before going to the next quadrant in the series, he re-sterilized the loop and cooled it, then he dragged the loop across the previous quadrant into the next one. The purpose of streaking in this instance was to __________

reduce the concentration of the culture

increase the concentration of the culture

eliminate ambient bacteria from the environment

eliminate ambient bacteria from the culture

Answer 1

A pure culture is a culture of a single strain of organism, without the contamination from other strains of organisms. For isolation of pure culture, techniques used can be:

a. Streaking- It involves various streaking patterns using sterile loop, with thinning out of the inoculum, at end of a streak.

b. Pour plate method- Pouring different dilutions of culture on sterile media plates.

c. spread plate method- Using sterile spreader to spread different dilutions on sterile media plates.

d. Serial dilution method- Using sterile pipette, diluting culture from stock sample to further dilutions of sterile water or broth.

e. Single cell isolation methods- a single colony of culture is picked either using capillary pipette method or micromanipulator method.

Answer: reducing the concentration of the culture.