CLED Agar- Composition, Principle, Preparation, Results, Uses


CLED Agar is an acronym for Cystine Lactose Electrolyte Deficient Agar. It is a type of differential and selective culture medium that is commonly used for the isolation and enumeration of bacteria from urine specimens. It is especially useful for the detection of urinary tract infections (UTIs) caused by members of the family Enterobacteriaceae, such as Escherichia coli, Klebsiella, Proteus, and others.

CLED Agar was first developed by Sandys in 1960 as a modification of MacConkey Agar, which is another differential and selective medium for enteric bacteria. The main difference between CLED Agar and MacConkey Agar is that CLED Agar does not contain any electrolytes (such as sodium chloride) or bile salts. These components are known to inhibit the growth of some urinary pathogens, such as Proteus species, which can produce urease and alkalize the medium. CLED Agar also contains L-cystine, which enhances the growth of some coliforms that require this amino acid.

CLED Agar has a green color due to the presence of bromthymol blue, which is a pH indicator that changes color depending on the acidity or alkalinity of the medium. The medium turns yellow when lactose-fermenting bacteria grow on it, indicating acid production. The medium remains green or turns blue when non-lactose-fermenting bacteria grow on it, indicating no acid production or alkaline reaction. CLED Agar also allows the differentiation of some bacteria based on their colony morphology and size. For example, E. coli produces large yellow colonies with a dark center, while Proteus produces small translucent colonies with a characteristic swarming pattern.

CLED Agar is widely used in clinical microbiology laboratories as a primary screening tool for urine culture. It can help identify the presence and type of bacteria in urine samples and guide further diagnostic tests and treatment options. CLED Agar is also suitable for long-term storage and transport of urine specimens without compromising their viability or quality. However, CLED Agar has some limitations that need to be considered when interpreting the results. For instance, some bacteria that cause UTIs may not grow well or at all on CLED Agar, such as streptococci, Neisseria gonorrhoeae, and other fastidious organisms. Therefore, other culture media and methods may be required to detect these pathogens. Moreover, CLED Agar does not provide sufficient information for the complete identification of bacteria, which may require additional biochemical and serological tests.