Tryptic Soy Agar with Lecithin and Tween® 80 is recommended for use in the detection and enumeration of microorganisms in replicate plating techniques. Also used for the detection and enumeration of microorganisms present on the surfaces of sanitary importance.

Principles The formulation of Tryptic Soy Agar with Lecithin and Tween® 80 is prepared according to the United States Pharmacopeia (USP) standard formula for Soybean-Casein Digest Agar Medium. It is also included in approved procedures in the Compendium of Methods for the Microbiological Examination of Foods and in Standard Methods for the Examination of Water and Wastewater.

Tryptic Soy Agar with Lecithin and Tween® 80 contains digests of soybean meal and casein which provides amino acids and other nitrogenous compounds making it a nutritious medium for many microorganisms. Sodium chloride is added to maintain the osmotic equilibrium. Dextrose is added to serve as an energy source. Quaternary ammonia compounds are neutralized by lecithin while phenolic disinfectants and hexacholorophene are neutralized by Tween® (polysorbate) 80. Together, lecithin and Tween® (polysorbate) 80 neutralize ethanol.

This medium may be supplemented with blood to provide a more nutritious medium for fastidious organisms, or with antimicrobials to provide a selective medium for specific organisms out of a mixed flora sample.