The loop is sterilized after the initial inoculum is put on to avoid contamination of other microbes or impurities.

What is used to sterilize inoculating loop needle?

The inoculating loop is sterilised by passing it at an angle through the flame of a gas burner until the entire length of the wire becomes orange from the heat. In this way all contaminants on the wire are incinerated.

What is the purpose of flame sterilizing the mouth of the test tube during inoculation?

Flaming the Mouth of the Test Tube: Passing the mouth of a tube through the flame of a Bunsen burner creates a convection current which forces air out of the tube. This prevents airborne contaminants from entering the tube.