CLED Agar (Cystine Lactose Electrolyte Deficient) is a non-selective differential plating medium for the growth and enumeration of urinary tract microorganisms. Omitting sodium chloride inhibits the Proteus swarming and supports the growth of the vast majority of bacteria causing urinary tract infections, and is used to differentiate and identify them. The presence of bacterial contaminants like Diphtheroids, Lactobacilli and other microbes indicate the degree of care taken with the handling of the urine specimen. The microorganisms which cause infection in the urinary tract are generally abundant and of only one species. E. coli is the organism most frequently isolated. Beef Extract and Casein peptone provide nitrogen, vitamins, minerals and amino acids essential for growth. Lactose is the fermentable carbohydrate providing carbon and energy. L-Cystine is added as a growth supplement for cystine dependent coliforms. Differentiation of lactose fermenters and lactose non fermenters is achieved using bromothymol blue as a pH indicator. Organisms that ferment lactose will lower the pH and change the color of the medium from green to yellow. Bacteriological agar is the solidifying agent.
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