CLED agar

CLED agar

CLED agar (Cystine–Lactose–Electrolyte-Deficient agar) is a type of microbiological culture media used in the identification and differentiation of urinary tract infections (UTIs). It is particularly useful for the cultivation of bacteria from urine samples, as it supports the growth of most urinary pathogens while inhibiting the swarming of Proteus spp., a common contaminant that can obscure other colonies on the plate.

Composition

CLED agar contains cystine and lactose as the primary sources of nutrients. Cystine serves as a growth enhancer for certain bacteria, while lactose is a fermentable carbohydrate that allows for the differentiation of lactose-fermenting from non-lactose-fermenting organisms. The medium is electrolyte-deficient to prevent the swarming of Proteus species, which require certain electrolytes for their characteristic swarming motility. Additionally, it contains agar as the solidifying agent and indicators such as bromothymol blue, which changes color in response to pH changes, facilitating the identification of fermenting organisms.

Purpose and Use

The primary use of CLED agar is in the diagnosis of UTIs. It allows for the isolation and enumeration of bacteria in urine samples, providing valuable information for the diagnosis and treatment of infections. The differentiation between lactose-fermenting and non-lactose-fermenting organisms on CLED agar can help in the preliminary identification of the causative agents of UTIs. For example, Escherichia coli, a common cause of UTIs, is a lactose fermenter and will produce yellow colonies on CLED agar due to acid production from lactose fermentation.

Advantages

One of the main advantages of CLED agar is its ability to inhibit the swarming of Proteus species, making it easier to isolate and identify other bacteria present in the sample. Additionally, the medium supports the growth of a wide range of urinary pathogens, making it a versatile tool in the microbiology laboratory. The color change associated with lactose fermentation also provides a simple and effective means of differentiating between organisms, aiding in the identification process.

Limitations

While CLED agar is useful for the isolation and preliminary identification of urinary pathogens, further testing is often required to fully identify and characterize the organisms present. This may include biochemical tests, serotyping, or molecular methods.

Preparation and Storage

CLED agar is commercially available in dehydrated form and must be prepared according to the manufacturer's instructions. Typically, this involves dissolving the dehydrated medium in distilled water, autoclaving to sterilize, and then pouring into petri dishes to solidify. Prepared plates should be stored in a refrigerator and used within a specified period to ensure the medium's efficacy.

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