what is the purpose of heat fixation for the bacterial smear?
Heat fixation is the procedure used to adhere a bacterial smear to a glass slide for viewing by a compound microscope. It denatures the protiens on the surface of the bacteria causing them to be sticky.
After a smear has been allowed to dry at room temperature, the slide is gipped by tongs or a clothespin and passed through the flame of a Bunsen burner several times to heat-kill and adhere the organism to the slide. Heat fixation cannot be used in the capsular stain method as heat fixation will shrink or destroy the capsule (glycocalyx) and cannot be seen in stains.
Sterlizing of the inoculation loop is essential in order to avoid contamination of the slide preparations and also to prevent contamination of the inoculum plate.
You want to sterilize the innoculating loop before you do a smear because you want to kill off any other bacteria that might have been on the loop, such as something that landed on it while you were preparing your materials. You only want the bacteria from your sample to be on the loop.