Gelatinase Test

Nutrient gelatin is a differential medium that tests the ability of an organism to produce an exoenzyme, called gelatinase, that hydrolyzes gelatin.

Gelatin is commonly known as a component of gelled salads and some desserts, but it's actually a protein derived from connective tissue. When gelatin is at a temperature below 32°C (or within a few degrees thereof), it is a semisolid material.  At temperatures above 32°C, it is a viscous liquid. 

Gelatinase allows the organisms that produce it to break down gelatin into smaller polypeptides, peptides, and amino acids that can cross the cell membrane and be utilized by the organism.

When gelatin is broken down, it can no longer solidify.  If an organism can break down gelatin, the areas where the organism has grown will remain liquid even if the gelatin is refrigerated.

If the gelatin is liquid when it comes out of the refrigerator, the organism is gelatinase positive. Important: When the gelatin comes out of the incubator, it will be liquid whether the organism is gelatinase positive or negative. Why is this?

The gelatinase test can be used to differentiate between Staphylococcus aureus and Staphylococcus epidermidis. It can also be used to differentiate Serratia marcescens, Proteus vulgaris, and Proteus mirabilis from other enterics.