Question

Discuss, how is it possible to isolate both aerobes and anaerobes using streak plates?

Answer 1

Anaerobes are those organisms which can't survive in the presence of O2. Aerobes are those bacteria which need O2 for their survival. So , inorder to separate anaerobes from aerobes, O2 supply should be cut off for the bacteria. This kills aerobic bacteria. From a mixture of bacterial culture, you can separate anaerobic bacteria from aerobes by candle jar method.

Candle jar method is one simple method to isolate anerobes from aerobes. Place the streak plates in a jar with burning candle. Close the lid of the jar and seal the lid with vaseline, so that fresh air does not get in. After incubating the plate , the bacteria that are growing are the anaerobic bacteria. The burning candle consumes all the O2 and burning candle stops burning too. That is the indication that the anaerobic conditions are created. This is how we can isolate anaerobes from aerobes.

Same streak plate if you place in incubator with normal air, obligate anaerobes will die and only aerobes will grow. O2 is toxic to anaerobic bacteria like Clostridium, Actinomyces etc.