BacterTube™ Lysin decarboxylase (LDC)

The test medium used to differentiate Salmonella arizona from the Bethesda Ballerup group of Enterobacteriaceae.
Code: 08030
Packaging: 50 tubes/ box or as per customer request.
Storage Conditions: 2–8°C.
Transportation: Ambient temperature.
Shelf Life: 6 months from the date of manufacture.

INTENDED USE

BacterTube™ Lysin decarboxylase (LDC) is recommended for differentiating Salmonella arizonae from the Bethesda Ballerup group of Enterobacteriaceae.

PRINCIPLES

BacterTube™ Lysin decarboxylase (LDC) is based on the original decarboxylase media described by Moeller for detecting lysine and ornithine decarboxylase as well as arginine dihydrolase. It was later adapted by Falkow to aid in the identification and differentiation of Salmonella and Shigella. The medium is particularly suited for studying decarboxylase activity in members of the Enterobacteriaceae family, except for Klebsiella and Enterobacter.
This medium is recommended by the American Public Health Association (APHA) and other standard microbiological methods for evaluating decarboxylase activity.
When organisms are inoculated into Lysine Decarboxylase Broth:
- During the initial incubation phase, fermentation of dextrose generates acid, which lowers the pH and causes the bromocresol purple pH indicator to turn yellow.
- The acidic environment stimulates the activity of lysine decarboxylase, resulting in the decarboxylation of lysine to cadaverine.
- The production of cadaverine creates an alkaline environment, which causes the pH indicator to revert from yellow to purple.
- If the organisms do not produce the decarboxylase enzyme, the medium remains yellow, indicating no alkaline change.
- Non-fermenters of dextrose will show no change in medium color, maintaining the original purple appearance.
The test should be conducted with a light inoculum, and results should not be interpreted before 24 hours of incubation. Some organisms may require an extended incubation period of up to 4 days to demonstrate decarboxylase activity.

Allow the BacterTube™ Lysine Decarboxylase (LDC) medium tubes to reach room temperature.
Use a sterile inoculating tool to collect the bacterial culture.
Inoculate by stabbing into the center of the medium.
Add 1–2 drops of sterile mineral oil to the surface of the inoculated tubes to create an anaerobic environment.
Incubate the tubes for 24 – 48 hours at 35 ± 2°C under aerobic conditions.

RESULTS

Observe the results and interpret as per the color change:
- Purple: Positive Lysine Decarboxylase: Alkaline conditions induced by the production of cadaverine cause the bromocresol purple indicator to change from yellow back to purple. This indicates that the organism can produce the decarboxylase enzyme.
- Yellow: Negative Lysine Decarboxylase: If the organism does not produce the decarboxylase enzyme, the color of the medium will remain yellow.

BacterLab ensures the quality of each product batch by testing with ATCC reference strains.

Reference strain	Incubation conditions	Expected result
E.coli ATCC 25922	18 – 24 hours at 35 – 37⁰C, aerobic	Positive, purple
Klebsiella aerogenes ATCC 13048		Positive, purple
Klebsiella pneumoniae ATCC 13883		Positive, purple
Proteus mirabilis ATCC 25933		Negative, yellow
Salmonella Typhi ATCC 6539		Negative, yellow