Fluid selenite cysteine Medium (twin pack)

 Principle

• Fluid Selenite Cystine Medium is a modification of Leifsons (1936) formula with added cystine by North and Bartram (1953). The medium is composed of tryptone, lactose, L-Cystine, sodium selenite, and sodium phosphate.
• Tryptone provides nitrogen and amino acids. Lactose is a fermentable carbohydrate. Sodium selenite is a selective agent and inhibits the growth of gram-positive and many gram-negative organisms.
• Although the sodium selenite is reduced by bacterial growth, and rise in pH takes place which leads to a decrease in the selectivity of selenite. Since lactose is added into the medium, due to lactose fermentation acid is produced and maintains neutral pH.
• The decrease in pH due to the reduction of selenite is compensated by the acid produced by lactose fermentation.  Sodium phosphate provides phosphate for growth and helps in the maintenance of the pH if the medium.
• L-cystine maintains ambient redox potential, which enhances and improves recovery of Salmonellae and a few Shigella sp. from food and dairy products or processed products.

 Use: Recommended for enrichment and isolation of Salmonella and Shigella from food, dairy products, and clinical specimens in accordance with United States Pharmacopoeia.