Question

summarize how to do the gelatin liquefaction test and why it works.

Answer 1

Gelatin is a solidifying agent usually using in the food industry. Gelatin liquefaction test is used to identify the gelatinases ( ability to hydrolyze gelatin) activity of bacterias. It essentially shows the proteolytic action of bacteria. There are 2 steps for the complete hydrolyzing reaction of gelatin. First, the gelatin will convert to numerous polypeptides and then hydrolyzed to amino acids. So that these amino acids can be taken up by the bacteria for their metabolism. Gelatin liquefaction test mostly used to detect the ability of an organism to produce gelatinases, to distinguish between gelatinase positive and gelatinase negative bacteria.

Procedure: Inoculate the test bacteria to gelatin-rich medium and keep at the optimal growth temperature of the test bacteria for up to 2 weeks (mostly 37°C, or better at 25°C if the organism grows at 25°C than at 37°C). Remove the tubes from the incubator daily to check the gelatinase activity. Keep the tubes in an ice bath at 4°C for 15-30 minutes or at least the control tube solidifies.

Result: gelatin usually liquifies at 28°C and above. So partial or complete liquefaction of the media in the inoculated tube at an ice bath shows the gelatinase activity. Control will continue solidified even after exposure to an ice bath.

Inference: liquefaction of the inoculated tube shows that test bacteria is gelatinases positive. It consuming gelatin from the media for its metabolic needs. Consumption of gelatin reduces the gelatin content of the media and so the solidification ability of the media even in a lower temperature.