Isolation and preservation methods for pure cultures || Microbiology || 3rd semester || Exam Guidance ||

 

Isolation and preservation methods for pure cultures

Isolation and preservation methods for pure cultures are essential in microbiology and other fields of research. These methods allow scientists to obtain and maintain a single species of microorganism for further study and experimentation. Here are some commonly used techniques:

Isolation Methods:

1. Streak Plate Method: This is a widely used technique where a small amount of the mixed culture is streaked over the surface of a solid agar medium in a petri dish. Through serial dilution and spreading, individual colonies of different microorganisms are obtained, each arising from a single cell or a group of identical cells.
2. Pour Plate Method: In this method, a known volume of a diluted mixed culture is added to molten agar medium and mixed well. The mixture is then poured into petri dishes and allowed to solidify. Colonies develop both on the surface and within the agar, allowing isolation of individual colonies.
3. Spread Plate Method: Similar to the streak plate method, the spread plate method involves spreading a diluted culture over the surface of an agar plate using a sterile spreader. The goal is to obtain well-isolated colonies that can be picked and cultured separately.

Preservation Methods:

1. Refrigeration: Storing cultures at low temperatures, typically around 4°C (39°F), can slow down microbial growth and prolong the viability of cultures for several weeks to a few months. This method is suitable for short-term storage.
2. Freezing: Cultures can be preserved by freezing them at temperatures below -20°C (-4°F) or using liquid nitrogen (-196°C or -320.8°F). Before freezing, a cryoprotective agent like glycerol or dimethyl sulfoxide (DMSO) is added to protect the cells from damage caused by ice crystal formation.
3. Lyophilization (Freeze-drying): This method involves removing water from the culture under vacuum conditions. The culture is frozen and then subjected to sublimation, where water is directly converted from the solid (ice) phase to the gas phase. The resulting lyophilized culture can be stored at room temperature for an extended period and rehydrated when needed.
4. Microencapsulation: In this method, individual cells or small aggregates of cells are encapsulated in a protective matrix, such as alginate beads or microspheres. These microcapsules can be stored in a suitable medium or lyophilized for long-term storage.

It's important to note that different microorganisms may have specific requirements for isolation and preservation, and the choice of method may depend on factors such as the nature of the microorganism, intended storage duration, and available resources.