TTC Lecithin Tween 80 Nutrient Agar
This dehydrated culture medium is specially formulated for the enumeration of total aerobic bacteria in cosmetic samples. Lecithin and Tween 80 act as neutralizers to offset the bacteriostatic effect of preservatives in cosmetics, ensuring accurate recovery of target bacteria. TTC in the medium turns bacterial colonies red for easy counting and reduces swarming spread of certain strains.
Composition (g/L)
Peptone 20.0
Beef extract 3.0
Sodium chloride 5.0
Lecithin 1.0
Tween 80 7.0
Agar 15.0
pH: 7.1–7.2 at 25 ℃
Verification Principle
Peptone and beef extract supply carbon, nitrogen, vitamins and essential growth factors for bacterial propagation. Sodium chloride maintains suitable osmotic pressure. Lecithin neutralizes quaternary ammonium salt preservatives, while Tween 80 neutralizes phenols, hexachlorophenol and formalin; the combination of lecithin and Tween 80 can neutralize ethanol. Agar serves as the gelling agent. TTC is reduced by most bacteria to produce clearly visible red colonies and suppresses swarming growth of some bacterial species.
Directions for Use
Weigh 51.0 g of the medium powder, heat to dissolve in 1000 mL distilled water, dispense 200 mL per bottle, autoclave at 121 ℃ for 15 min. Cool the sterilized medium to 50–55 ℃, add 2 mL of sterile 0.5% TTC solution, mix thoroughly and use.
Preparation of 0.5% TTC solution: Weigh 0.25 g TTC, dissolve in 50 mL distilled water, autoclave at 121 ℃ for 15 min, store in an amber bottle at 2–8 ℃.
Microbial Performance Test
Prepare the medium following the instructions. Inoculate specified quality control strains and incubate aerobically at 36 ± 1 ℃ for 48 ± 2 hours.
