Dulcitol – sugar fermetation test

Published by Johnson M on

Dulcitol is also known as Galactitol, a sugar alcohol derived through reduction of galactose.

Aim of the test

The purpose of dulcital ferementation test in microbiology is to determine if a given microorganism can ferment dulcitol as a carbon source. In the performance of biochemical properties of Salmonella, this test can be done. Salmonella does not ferment dulcitol.

Procedure for dulcitol fermentation test

Dulcitol, usually at concentrations between 0.5 to 1.0% is added to a broth, such as nurtrient brith or peptone water. A suitable pH indicator is usualy added to the medium to signify acid end products after fermentation. The broth is poured into testtubes with inverted durham tubes to indicate gas formation during fermentation. This media can then be sterilizedin a autoclave before innocuation. A pure culture of the isolate to be tested is then scooped and innoculated into the testube. Incubation at 35-37 C for 24 hours follows and the results are determined.

Testtubes with purple indicator in dulcitol broth

End results and interpretation

If dulcitol is fermented to produce acid end products, the pH of the medium drops and the pH indicator changes to signify such changes (positive). If a gas is produced, the durham tube traps it and can be seen as space developung in the inverted durham tube (gasing).

Positive samples (Yellow) and Negative (Purple)
Positive samples (Yellow) and Negative (Purple)
Gasing with no acidity development