Thermo Scientific™ Oxoid™ Cystine-Lactose-Electrolyte-Deficient (CLED) Medium (Dehydrated)

The Cystine-Lactose-Electrolyte-Deficient (CLED) Medium is a traditional and widely used diagnostic culture medium for the isolation, enumeration, and differentiation of urinary pathogens. This medium provides superior colony differentiation, diagnostic clarity, and prevents the swarming of Proteus species, making it an essential tool in urinary bacteriology.

Key Features

1. Effective Colony Differentiation

• Distinct colony appearances for various urinary pathogens:
  • Escherichia coli: Yellow opaque colonies.
  • Proteus spp.: Translucent blue colonies.
  • Salmonella spp.: Flat green colonies.
  • Staphylococcus spp.: Deep yellow colonies.

2. Swarming Prevention

• The electrolyte-deficient formulation inhibits the swarming of Proteus spp., ensuring clearer and more interpretable results.

3. Non-Inhibitory Nature

• CLED Medium is non-inhibitory, allowing the growth of a wide range of urinary pathogens without suppressing specific groups.

4. Versatility in Techniques

• Successfully used in:
  • Plate cultures for routine urine analysis.
  • Dip-inoculum transport medium techniques for maintaining sample integrity during transport.
  • Media-coated slide techniques for rapid testing.

5. Clinically Reliable

• Ideal for routine differential viable counts in general practitioner and hospital settings, including:
  • Screening for asymptomatic bacteriuria.
  • Diagnostic use in antenatal specimens.

Applications

1. Clinical Diagnostics

• Isolate and identify urinary tract infection pathogens.
• Quantify bacterial load in urine samples.

2. Differentiation of Pathogens

• Distinguish between common urinary pathogens like E. coli, Proteus spp., Salmonella spp., and Staphylococcus spp.

3. Transport Media Techniques

• Maintain specimen integrity for delayed transport using the Dip-inoculum Transport Medium technique or media-coated slide techniques.

4. Antenatal Screening

• Screen for asymptomatic bacteriuria in pregnant patients to prevent complications.

Advantages

1. Ease of Use

• Clear colony differentiation makes it easy to identify urinary pathogens.

2. High Diagnostic Value

• Provides reliable and reproducible results for routine urinary bacteriology.

3. Swarming Inhibition

• Prevents Proteus spp. overgrowth, ensuring a clean and interpretable culture plate.

4. Versatility

• Adaptable to multiple diagnostic techniques and clinical settings.

Specifications

How It Works

1. Preparation:
   • Prepare the medium by rehydrating the dehydrated powder with distilled water and autoclaving as instructed.
2. Inoculation:
   • Inoculate the medium with urine specimens directly or using the Dip-inoculum technique.
3. Incubation:
   • Incubate at 35–37°C for 18–24 hours.
4. Interpretation:
   • Identify colonies based on their characteristic color and morphology.

Why Choose Oxoid™ C.L.E.D. Medium?

• Proven Performance: Widely recognized as a reliable medium for urinary bacteriology.
• Easy Interpretation: Facilitates pathogen differentiation with clear colony distinctions.
• Swarming Control: Effective prevention of Proteus spp. swarming for clean plates.
• Versatility: Adaptable to multiple diagnostic techniques and clinical settings.

The Thermo Scientific™ Oxoid™ C.L.E.D. Medium (Dehydrated) is an essential medium for urinary bacteriology, providing reliable, precise, and versatile solutions for routine diagnostics and advanced clinical applications.

C.L.E.D. Medium Alternatives

Cystine-Lactose-Electrolyte-Deficient (C.L.E.D.) Medium is widely used for urinary bacteriology, particularly for isolating, enumerating, and differentiating urinary pathogens. However, several alternative culture media are available that can serve similar purposes, depending on specific laboratory requirements or clinical objectives.

1. MacConkey Agar

• Purpose: Primarily used for isolating and differentiating Gram-negative bacteria.
• Features:
  • Lactose fermentation: Lactose fermenters produce pink colonies, while non-fermenters remain colorless.
  • Bile salts inhibit Gram-positive bacteria.
• Advantages:
  • Highly selective for Gram-negative organisms.
  • Distinguishes lactose fermenters (e.g., E. coli) from non-fermenters (e.g., Proteus).
• Limitations:
  • Cannot differentiate Gram-positive bacteria like Staphylococcus.
  • Does not inhibit Proteus swarming as effectively as C.L.E.D.

2. Chromogenic UTI Media

• Purpose: Specifically designed for urinary tract infection (UTI) pathogens.
• Features:
  • Chromogenic substrates enable color-based identification of multiple urinary pathogens in a single plate.
  • Identifies E. coli, Enterococcus spp., Klebsiella spp., Proteus spp., Staphylococcus spp., etc.
• Advantages:
  • Faster and more distinct colony differentiation.
  • Simplifies interpretation and reduces the need for additional tests.
• Limitations:
  • More expensive than traditional media.
  • May require careful storage and preparation.

3. Blood Agar

• Purpose: General-purpose medium for cultivating a wide range of bacteria.
• Features:
  • Supports the growth of both Gram-positive and Gram-negative organisms.
  • Can demonstrate hemolysis patterns (alpha, beta, gamma).
• Advantages:
  • Broad-spectrum growth.
  • Can differentiate hemolytic bacteria like Streptococcus spp.
• Limitations:
  • Not specific for urinary pathogens.
  • Does not prevent Proteus swarming.

4. Mueller-Hinton Agar

• Purpose: Primarily used for antimicrobial susceptibility testing but also supports bacterial growth.
• Features:
  • Non-selective and non-differential medium.
  • Allows growth of most non-fastidious organisms.
• Advantages:
  • Universal application for susceptibility testing.
  • Supports growth of a wide range of organisms.
• Limitations:
  • Cannot differentiate urinary pathogens.
  • Swarming of Proteus is not inhibited.

5. EMB (Eosin Methylene Blue) Agar

• Purpose: Used for isolating and differentiating Gram-negative bacteria, particularly lactose fermenters.
• Features:
  • Lactose fermenters (e.g., E. coli) produce dark colonies with a green metallic sheen.
  • Non-fermenters appear colorless or translucent.
• Advantages:
  • Highly effective for identifying E. coli in urine samples.
• Limitations:
  • Not suitable for Gram-positive organisms.
  • Less effective in preventing Proteus swarming.

6. UTI-Specific Broths

• Purpose: Liquid media for isolating and enumerating urinary pathogens.
• Examples:
  • Urea Broth: Detects urease-producing organisms like Proteus.
  • Tryptone Soya Broth: General enrichment for bacterial growth.
• Advantages:
  • Useful for quantitative urine cultures.
• Limitations:
  • Requires additional steps (e.g., subculturing) for identification.

Comparison of C.L.E.D. with Alternatives

Conclusion

• C.L.E.D. Medium remains the preferred choice for routine urinary bacteriology due to its ability to differentiate key pathogens and prevent Proteus swarming.
• Chromogenic UTI Media offers faster and more precise results but at a higher cost.
• MacConkey Agar or EMB Agar are suitable for laboratories focusing on Gram-negative pathogens.
• Blood Agar is ideal for general bacteriology but lacks specificity for urinary pathogens.

The choice of alternative depends on clinical requirements, budget, and the target pathogen spectrum.