Letheen Broth Base Modified ISO 21149 is a dehydrated medium designed for the microbiological testing of cosmetics. Its formulation is in accordance with ISO 21149, ensuring high standards for quality control in the cosmetics industry.
Composition and Principle
The Letheen Broth Base Modified contains a blend of Peptone, Tryptone, Meat Extract, Yeast Extract, Sodium Chloride, Lecithin, and Sodium Bisulfite, with a final pH of 7.2 ± 0.2. This medium provides essential nutrients for microbial growth, with Peptone, Tryptone, and Meat Extract serving as nitrogen sources. Yeast Extract is a source of amino acids and B vitamins, while Sodium Chloride maintains the osmotic balance. The unique components, Lecithin, and Sodium Bisulfite, are included to neutralize the preservatives commonly present in cosmetics, making this medium ideal for testing cosmetic products.
To prepare the medium, 37.8 g of the powder is suspended in 1 liter of distilled or deionized water. After adding 5 mL of Tween 80, the mixture is heated until completely dissolved, dispensed into final containers, and then sterilized in an autoclave at 121°C for 15 minutes.
Technique and Application
The testing technique involves inoculating 9 mL of the prepared Letheen Broth Base Modified with 1 g or 1 mL of the cosmetic sample. If high levels of contamination are expected, larger volumes of broth can be used. The suspension is mixed well and incubated at 32.5 ± 2.5°C for at least 20 hours. After incubation, a portion of the suspension is transferred onto a nutritive medium plate and spread evenly. The plate is then incubated at the same temperature for 48-72 hours.
Interpretation of Results
The results are expressed as Colony Forming Units (CFU) per gram or milliliter of the sample. This is done by counting the colonies on the plate and multiplying by the dilution factor.
Storage and Handling
The dehydrated medium should be stored at 10-30°C away from light and used before the expiry date on the label or if signs of deterioration or contamination are evident. The prepared medium must be stored at 2-8°C.
Warnings and Precautions
This product is not classified as hazardous under current legislation and does not contain harmful substances in concentrations of ≥1%. However, it must be used only by properly trained operators.
Letheen Broth Base Modified ISO 21149 is an essential medium for the microbiological testing of cosmetics, ensuring the safety and quality of cosmetic products. Its specific formulation effectively neutralizes cosmetic preservatives, enabling accurate detection and enumeration of aerobic mesophilic bacteria in these products.