Gelatin cannot pass trough bacterial cell wall and thus bacteria must catabolize them into smaller components using exocellular
enzymes (gelatinase). Test detects the ability of the organism to produce enzymes which hydrolyze gelatin.
MEDIUM PREPARATION: add 10-15g gelatin to 100 ml nutritive broth (heated to
Prepare a solution from one egg white (albumen) into 50 ml distilled water. Add this
solution drop by drop to 1000 ml gelatin nutritive broth (heated to 55 ˚C). Mix well then
raise temperature to 115 ˚C. Albumen coagulate and clarify the medium.
Filter trough cotton and distribute medium in tubes. Sterilize 20 minutes at 110 ˚C.
Hold tubes vertically until solidification. Normally, gelatin is solid under 20 ˚C and
liquid over 28 ˚C.
Inoculate a gelatin tube by stabbing the medium down the bottom. Incubate at 22 ˚C,
12 days, controlling liquefaction after 1st, 10th and 12th day. If bacteria do not grow at
22 ˚C then incubate at 37 ˚C but you need to cool the tube by refrigeration before
Liquefaction usually occurs at the surface of the medium. Viscosity of the medium increases in prolonged storage.
1. H. Raducanescu, V.Bica-Popii,1986. Bacteriologie veterinara, Ed. Ceres, Bucuresti.
2. PML Microbiologicals, Technical data sheet #370, Jan 2001.
COMPOSITION: agar 0.4%, gelatin, pH 7.2
Frazier reactive: HgCl2 15g, HCl 20 ml, distilled water 100 ml.
Pour medium in Petri dishes and disperse culture on surface. Incubate 2 to 14 days. Cover culture with 8-10 ml of Frazier reactive.
Non-hydrolysed gelatin forms a white, opaque precipitate. Liquefied gelatin appears as clear area around colonies.
Nutrient gelatin: pancreatic digest of gelatin 5 g, beef extract 5 g, gelatin 120 g, distilled water ad 1000 ml.
Gelatin 0.4%: gelatin 4g, distilled water ad 1000 ml.
(c) Costin Stoica