Techniques for Isolation of Pure Cultures

Pure or axenic cultures consist of a single type of microorganism. They are essential for studying the characteristics of individual species.

The streak-plate method isolates pure colonies on solid media. A loopful of sample is streaked across the agar surface in successive zones.

Each streak reduces cell density, enabling isolated cells in the terminal zone to form distinct colonies.

The spread-plate method uses a sterile spreader to evenly distribute a diluted microbial suspension on an agar surface, allowing distinct colonies to form from individual cells.

In the pour-plate technique, the diluted microbial suspension is added to a sterile plate, then sufficiently cooled molten agar is poured on top and mixed.

This way, the colonies grow within and on the agar surface, making the technique useful for isolating aerobic and anaerobic organisms.

Diatom-like microorganisms are cultured in liquid media. Pure cultures are obtained through selective enrichment or serial dilutions until a single organism is obtained. Their purity is verified post-incubation using techniques like microscopy.