Lysine Decarboxylase Medium ISO

When the medium is inoculated with a bacterium that is able to ferment dextrose, the acid produced lowers the pH of the medium and changes the color of the indicator from purple to yellow. The acidic condition also stimulates decarboxylase activity. The bacteria that decarboxylate the L-lysine to cadaverine are identified by the presence of a purple-red color. The production of these amines elevates the pH of the medium. A yellow color after 24 hours indicates a negative result, such as Yersinia.

Yeast extract is the source of vitamins, particularly of the B-group, essential for growth. Dextrose is the fermentable carbohydrate. Bromocresol purple is the pH indicator. Lysine is added to detect the production of the specific enzyme.

Typical formula in g/L, adjusted and/or supplemented as required to meet performance criteria.

Preparation

Suspend 9 grams of the medium in one liter of distilled water. Mix well and dissolve by heating with frequent agitation. Boil for one minute until complete dissolution. Dispense quantities of 5 mL into screw-capped tubes. Sterilize in autoclave at 121 °C for 15 minutes.

According to ISO 6579

According to ISO 6579 for the confirmation of Salmonella spp. in food, animal feed, animal feces and environmental samples:

1. Obtain presumptive colonies after inoculating the sample in selective isolation media such as XLD Agar (LC-1274) or other complementary ones (Chromogenic Salmonella Agar (LC-1122), Brilliant Green Agar (LC-1143), Bismuth Sulfite Agar (LC-1011), DCLS Agar (LC-1045), Deoxycholate Citrate Agar (LC-1067), Hektoen Enteric Agar (LC-1030), Salmonella Shigella Agar (LC-1064) and XLT4 Agar (LC-1159)).
2. To confirm Salmonella spp., inoculate the presumptive colonies at least in the Triple Sugar Iron Agar (LC-1172), Urea Agar (LC-2180) and the Lysine Decarboxylase Medium.
3. Inoculate the Lysine Decarboxylase Medium just below the surface of the liquid medium.
4. Incubate at 37 °C for 24 ± 3 h.
5. The turbidity and a purple color of the medium after incubation indicate a positive reaction. A yellow color indicates a negative reaction.

According to ISO 19250

According to ISO 19250 for the confirmation of Salmonella spp. in water samples:

1. Obtain presumptive colonies after inoculating the sample in selective isolation media such as XLD Agar (LC-1274) or other complementary ones (Brilliant Green Agar (LC-1143) or Bismuth Sulfite Agar (LC-1011)).
2. To confirm Salmonella spp., inoculate the presumptive colonies at least in the Triple Sugar Iron Agar (LC-1172), Urea Agar (LC-2180) and the Lysine Decarboxylase Medium.
3. Inoculate the Lysine Decarboxylase Medium well below the surface of the liquid medium and incubate at 36 ± 2 °C for 24 ± 3 h.
4. Typical Salmonella cultures show a purple colour after incubation.

According to ISO 10273

According to ISO 10273 for the confirmation of Yersinia enterocolitica:

1. Obtain presumptive colonies after inoculating the sample in a selective isolation medium such as the Selective Agar Base for Yersinia CIN (LC-1126).
2. Inoculate the colonies in the Lysine Decarboxylase Medium just below its surface.
3. Incubate at a temperature of 30 °C for 24 ± 2 hours.
4. The appearance of a violet color after incubation indicates that the reaction is positive. If the color is yellow, the reaction will be negative.

• ISO 6579 Microbiology of food and animal feeding stuffs - Horizontal method for the detection of Salmonella spp.
• ISO 10273: Microbiology of food and animal feeding stuffs - Horizontal method for the detection of presumptive pathogenic Yersinia enterocolitica.
• Falkow A. S. Clin. Path. 28:598, 1958.
• Ewing Davis and Deaves, Studies in the Serratia Group. U.S. Dept. H.E.W.C.D.C. Atlanta, 1972.
• Edwards and Ewing. Identification of Enterobacteriaceae, Burgess Publ. Co. Minneapolis, Minn., 1961.
• ISO 19250 Water quality - Detection of Salmonella spp.