Which laboratory method is best for isolating specific bacteria from a mixed culture?

Streak plating is the most effective method for isolating specific bacteria from a mixed culture due to its ability to separate individual bacterial cells on an agar plate. The technique involves using a sterile inoculating loop to spread a diluted sample of the mixed culture across the surface of the agar in a specific pattern. As the loop is dragged across the agar, the number of bacteria decreases, leading to the eventual growth of isolated colonies from single cells.

This method allows for the separation and proliferation of individual bacterial species from a heterogeneous mixture, which can then be easily identified based on colony morphology or further analyzed using additional methods. It is a fundamental technique in microbiology that facilitates the study of pure cultures, important for research and diagnostic purposes.

The other options have different applications and limitations in the context of isolating specific bacteria. Filtration is typically used for separating bacteria from liquids based on size but does not promote the growth of isolated colonies. Electrophoresis is used for separating proteins or nucleic acids rather than whole organisms, and microscopy is mainly used for visualizing cells rather than isolating them from mixed cultures. These methods do not provide the same capability to culture and identify isolated bacteria as streak plating does.