Isolation of pure cultures from mixed populations

Section 1: The Basics of Pure Cultures

Pure cultures consist of only one type of organism, which are essential for studying the characteristics of individual bacterial strains.
Isolation of pure cultures from mixed populations often involves culturing microbes under laboratory conditions where growth of one type of microbe is favoured.

Section 2: Techniques for Obtaining Pure Cultures

The streak plate method is one popular technique where the researcher uses a sterilised loop to streak microbes onto an agar plate, with successive streaks further diluting the sample.
The spread plate method involves spreading a dilute bacterial mixture over a solid medium, allowing isolated cells to grow into discrete colonies.
For liquid broth dilution technique, the diluted bacterial mixture is added to liquid broth and incubated. Tubes showing growth will contain only one type of bacteria.

Section 3: Identifying and Selecting Colonies

Once the bacteria have grown into visible colonies, researchers can choose an isolated colony and sub-culture it in a new medium to obtain a pure culture.
Each colony on the plate contains descendants of a single cell and is a pure culture.
Colonies can be identified by characteristics such as colour, texture, edge properties and elevation.

Section 4: Benefits of Obtaining Pure Cultures

Working with pure cultures allows scientists to study a microorganism’s characteristics in detail and make accurate observations without the interference from other organisms.
Pure cultures can be used to produce microbial products such as antibiotics or enzymes in industrial microbiology.
In medical settings, isolation of pure cultures aids in diagnosing infections and determining a microorganism’s sensitivity to antibiotics.

Section 5: Precautions in Obtaining and Maintaining Pure Cultures

Strict aseptic techniques must be practised to prevent contamination of the culture and influence of unexpected microbes.
Pure cultures should be periodically checked for purity, any unexpected changes in appearance may indicate contamination.
Proper incubation conditions (temperature, pH, oxygen levels, etc.) must be ensured for the growth of desired organisms and storage of pure cultures.