Overview
The metabolism of a glucide might follow the oxidative or the fermentative pathway. In the oxidative pathway the final electron acceptor must be the oxygen and therefore the process is aerobic and it produces a small amount of acidity, while in the fermentative pathway the final electron acceptor is an organic compound and the process is anaerobic, which produces a lot of acidity in a short amount of time.

The fermentation or the oxidation of the glucide can be seen in two test tubes with a glucoside culture medium, one open (aerobic) and the other one closed with paraffin (anaerobic).

For this test the semisolid Hugh-Leifson medium is used to which glucose is added in order to see whether this sugar is metabolized through the oxidative or fermentative pathway.

Carrying out the practical
A stab culture is formed by inoculating the semisolid medium of the two test tubes.

A small amount of sterile paraffin is added to one of them, and they are both incubated at 37ºC for 24 hours.

If the pathway is oxidative, only the open tube will turn slightly yellow on the top part. If the pathway is fermentative it turns a deep yellow that starts at the bottom of the two test tubes.

Recently inoculated medium	Oxidative pathway	Fermentative pathway Fernando Ramón-Borja & Sergio Cabot

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