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Laboratory Preparations/Biological Extracts

BILE SALTS

Code: LP0055

A standardised bile extract, consisting mainly of sodium glycocholate and sodium taurocholate, for use as a selective inhibitory agent in bacteriological culture media such as MacConkey Agar CM0007 and MacConkey Broth CM0005. Bile Salts LP0055 conforms to bacteriological requirements and batches are standardised, with respect to inhibitory properties, by the method of Burman1. It is generally employed in culture media at a concentration of 5 grams per litre. Bile Salts LP0055 meets the following specification:
Appearance - a 2% aqueous solution is light straw coloured, clear and free from extraneous matter.
Reaction - (2% aqueous solution) - pH 6 ± 0.2.
Minimal Effective Concentration (Burman1) - 0.25% - 0.5%.
Bacteriological Performance - MacConkey Broth and Agar made up with LP0055 at the minimal effective concentration (MEC) support satisfactory growth of bile-tolerant organisms including pathogenic staphylococci. Gas production by clostridia in broths containing 0.5% of LP0055 is inhibited when the concentration is raised to 2%, as in Brilliant Green Bile (2%) Broth CM0031 thus eliminating false positives in the 44°C test for Escherichia coli. During the testing of milk for Escherichia coli with Brilliant Green Bile (2%) Broth, false positives due to milk lactobacilli do not occur if the medium contains LP0055.

Reference
1
. Burman N. P. (1955) Proc. Soc. Water Treat. Exam. 4. 10.

 
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