Download Gelatin liquefaction test

Done by : Huda Elsharatha
Number : 220050293
Dr Abdelrauf El manama
Principle:
Gelatin is a protein that is derived from collagen.
The gelatin molecule is to large to enter the cell as a
whole so the exoenzyme gelatinase
Purpose:
To differentiate between organisms that produce
the exoenzyme gelatinase and those that do
not
1. vibrio (vibrio cholera)
2. Pseudomonas (pseudomonas aeruginosa)
3. Serratia
vibrio
pseudomonas
serratia
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,
Gelatinase :enzyme that hydrolyzes gelatin
Two methods used to determine gelatinase
production
The gelatin stab method
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 30dys.
Whenever desired, the tube may be refrigerated
and results observed. If the tube is still negative
after 30days of incubation (completely solidifies
when refrigerated), it can be reasonably concluded
that this organism does not produce gelatinase.
1. Gelatin Stab Method
The tubes to the right depict a gelatinase negative (A) and gelatinase positive (B and C) reactions.
The 'Serratia marcescens' on the left is positive for gelatinase production, as
evidenced by the liquidation of the media. The 'Salmonella typhimurium' on the
right is negative, as evidenced by the solidity of the media.
RESULTS
Positive strong :liquefaction occurs with 3days
Positive weak :liquefaction occurs in 3-4 days
Negative :no liquefaction after 30 days
The Gelatin Strip Method
The gelatin strip method employs strips of clear blue
plastic covered with a gray-green coating of
gelatin
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.
2. Gelatin Strip Method