Exercise 5: Pure Culture Techniques

A pure culture contains:

a single microbial species

Pure culture techniques aim to do what?

dilute bacterial samples in order to separate individual cells that can grow into isolated colonies when plated

What type of media is typically used when trying to isolate microbes from a mixed culture?

general purpose media

Which media is preferred to obtain pure cultures, solid or liquid?

solid

What is an example of a solid general purposed media?

agar

Agar is derived from:

seaweed

Microbes can digest agar, T or F? If false, why?

false; b/c microbes cannot metabolize agar

The pour plate method can be used:

quantitative and non-quantitative

How is culture diluted in a pour plate?

diluted in a series of tubes, then poured in molten agar

Once diluted agar is mixed well:

it is poured into a empty sterile petri dish and allowed to solidify

Where do colonies grow in a pour plate?

on top, embedded, and underneath agar

Pour plate method is the best for isolation, T or F?

false; not the best b/c colonies can grow throughout the agar

A spread plate also uses molten agar, T or F?

false; the agar on a spread plate is already solidified

Where do colonies form on a spread plate?

only on the surface of the agar

How is the culture diluted for a spread plate?

through a series of tubes of sterile media

Isolation streak plate technique is also know as the:

3-zone method

An isolation streak is a pure culture, T or F

false; it is from mixed culture, hence not pure; multiple colonies from different bacteria will form

How many zones does the sample get plated across?

3

the purpose of this method is to:

separate single species from a mixed species population

a subculture of a species on an isolation streak is called the:

secondary streak

What are the zones in a isolation plate?

-Zone I

-Zone II

-Zone III

-Zone IIIB

Zone IIIB is also called Zone IV, T or F?

false

Where will/should you see isolated colonies?

Zone IIIB

Which zone is the smallest? Largest?

Zone I; Zone IIIB