MicroVision 
 
Gelatinase  
Gelatin causes liquids to solidify at temperatures below 28 degrees Celsius. At temperatures above 28 degrees C. gelatin is a liquid. Some bacteria produce gelatinase, a proteolytic enzyme that hydrolyzes gelatin. The hydrolyzed gelatin no longer has the ability to gel and thus remains a liquid, even if placed at temperatures below 28 degrees. The presence or absence of gelatinase can be used to aid in identification of certain bacteria.  Two methods used to determine gelatinase production are the gelatin stab method and the gelatin strip method. 

The Gelatin Stab Method

The gelatin stab method employs nutrient gelatin deep tubes that contain 12% gelatin. A heavy inoculum from a pure culture of the test organism is stabbed into the media. The gelatin media is incubated for at least 48 hours, and then placed into the refrigerator for approximately 30 minutes. If the gelatin is still intact (the bacteria did not produce gelatinase), the media will solidify in the refrigerator and a negative test result is recorded. If the organism has produced sufficient gelatinase, the tube will remain liquid (at least partially) and not solidify in the refrigerator. A positive test result is recorded.

Some organisms may produce gelatinase in rather small quantities. Thus, a tube with a negative gelatinase result should be reincubated for up to two weeks. Whenever desired, the tube may be refrigerated and results observed. If the tube is still negative after two weeks of incubation (completely solidifies when refrigerated), it can be reasonably concluded that this organism does not produce gelatinase. 

The Gelatin Strip Method

The gelatin strip method employs strips of clear blue plastic covered with a gray-green coating of gelatin (available from Key See Products, 2124 Sawtelle Blvd., Los Angeles, CA 90025). Upon incubation with a gelatinase producing bacteria, the gelatin coating is slowly hydrolyzed and the blue plastic strip becomes visible (a positive result). There will not be any blue plastic visible on the gelatin strip in an organism that is unable to produce gelatinase (a negative result). Some organisms may produce gelatinase in rather small quantities. Thus, a negative gelatin strip tube should be reincubated for up to two weeks. 

Positive and negative gelatinase results are shown below. Tubes in image 1 have been inoculated, incubated, and refrigerated for 30 minutes. Click on each image to see an enlarged version. 

1. Gelatin Stab Method 2. Gelatin Strip Method
 

© 1998