CLED Agar (Cystine–Lactose–Electrolyte-Deficient Agar)

CLED Agar (Cystine–Lactose–Electrolyte-Deficient Agar)
Differential Medium for Urinary Tract Pathogens

Catalog Number: AS-1176

Overview
CLED Agar (Cystine–Lactose–Electrolyte-Deficient Agar), also known as BROLACIN Agar or Bromothymol Blue Lactose Cystine Agar, is a differential, non-selective solid medium developed by Monsur (1961) for the isolation, enumeration, and presumptive identification of bacteria from urine specimens.

Its electrolyte-deficient formulation inhibits swarming by Proteus species, while cystine supports the growth of cysteine-dependent organisms. Lactose is the primary carbohydrate, and bromothymol blue serves as the pH indicator, allowing differentiation of lactose-fermenting and non-fermenting organisms. CLED Agar supports a wide range of Gram-positive and Gram-negative urinary pathogens and is widely used for routine urinalysis in clinical microbiology laboratories.

Applications
• Isolation and enumeration of urinary tract infection (UTI) pathogens from urine specimens
• Differentiation of lactose-fermenting and non-fermenting bacteria in urine cultures
• Quantitative urine culture and screening for asymptomatic bacteriuria
• Subculture from enrichment broths or direct plating prior to antimicrobial susceptibility testing

Key Features & Benefits
• Electrolyte-deficient formulation prevents Proteus swarming
• Cystine supplementation enhances recovery of fastidious urinary pathogens
• Bromothymol blue indicator enables clear differentiation of lactose fermenters and non-fermenters
• Supports growth of common urinary pathogens including Escherichia coli, Enterococcus spp., Klebsiella, Staphylococcus, and Proteus
• Smooth, opaque surface compatible with automated colony counting systems

Principle of the Medium
CLED Agar limits electrolyte concentration to suppress Proteus swarming, allowing discrete colony formation. Lactose fermentation leads to acid production, causing a colour change in bromothymol blue. Lactose-fermenting organisms produce blue-green colonies, while non-fermenters remain yellow or colourless. Cystine enhances the growth of organisms with increased sulfur requirements, improving recovery from urine specimens.

Typical Composition (per litre)
Gelatin Peptone – 14.0 g
Proteose Peptone – 4.0 g
Lactose – 10.0 g
Sodium Chloride – 5.0 g
Disodium Phosphate – 3.0 g
L-Cystine – 0.128 g
Agar – 15.0 g
Bromothymol Blue – 0.02 g

Final pH: 7.3 ± 0.2 at 25 °C

Preparation
Suspend 51.148 g of dehydrated medium in 1 L of purified or distilled water.
Heat with gentle agitation to boiling until completely dissolved; avoid overheating to prevent lactose caramelisation.
Autoclave at 121 °C (15 psi) for 15 minutes.
Cool to 45–50 °C and pour into sterile Petri dishes (20–25 mL per plate).
Allow to solidify and dry the surface briefly before use.

Prepared medium should appear greenish-blue, opaque, and homogeneous without precipitate.

Incubation
Inoculate using a calibrated loop (e.g., 0.001 mL) for quantitative urine culture.
Incubate aerobically at 35–37 °C for 18–24 hours.

Typical Colony Appearance
Lactose fermenters (E. coli, Klebsiella): blue-green colonies
Non-lactose fermenters (Proteus, Pseudomonas): yellow or colourless colonies
Swarming by Proteus spp.: inhibited

Storage & Stability
Dehydrated medium: Store at 10–30 °C in a tightly closed container, protected from moisture and light
Prepared plates: Store at 2–8 °C in sealed plastic bags and use within 4–8 weeks
Discard if dehydrated, contaminated, discoloured, or if indicator colour fades

Intended Use
For laboratory research and microbiological quality control use only.
Not for human or veterinary consumption.
Not for diagnostic use without appropriate validation.

Quality & Compliance
Manufactured under controlled conditions to ensure batch-to-batch consistency.
Suitable for routine urine culture and UTI screening.
Performance comparable to leading international CLED agar formulations.

Customs & Trade Information
HS / AHECC Code: 3821.00.00
Prepared culture media for the development or maintenance of microorganisms