Why do you have to flame sterilize the inoculating loop before and after using?

what is the purpose of heat fixation for the bacterial smear?
Answer:
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.

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You flame before to sterilize the loop to prevent contaminating the original culture source. You flame afterwards to sterilize the loop to kill any residual bacteria remaining on the loop.

It's kind of like cooking with clean dishes to start with then washing up the dishes you used to cook with.

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