Thermo Scientific™ Oxoid™ Macconkey Agar (Dehydrated), 500G

The Thermo Scientific™ Oxoid™ MacConkey Agar is a reliable differential culture medium designed for the detection, isolation, and enumeration of coliforms and intestinal pathogens in water, dairy products, and biological specimens. Recommended by the World Health Organization (WHO) and the Department of Health, this medium provides valuable diagnostic insights by differentiating organisms based on bile tolerance, colony morphology, and chromogenesis.

Key Features

1. Differential Capabilities

• Easy-to-Read Colony Differentiation:
  • Escherichia coli: Red, non-mucoid colonies.
  • Staphylococcus spp.: Pale pink, opaque colonies.
  • Pseudomonas aeruginosa: Green-brown colonies.

2. Broad Pathogen Coverage

• Cultivates pathogenic Gram-positive cocci (e.g., Staphylococci and Enterococci) as well as Gram-negative Enterobacteriaceae.
• Suitable for a variety of specimens, including:
  • Urine
  • Feces
  • Wound swabs

3. Balanced Selectivity

• While selective for Gram-negative bacteria, it permits the growth of certain Gram-positive organisms, making it ideal for mixed flora cultures.
• Complements other selective media (e.g., Desoxycholate Citrate Agar, Brilliant Green Agar) to provide a comprehensive analysis.

4. Standardized and Reliable

• Recognized by the WHO and health departments for water and food testing.
• Provides consistent performance in the cultivation and differentiation of pathogens.

Applications

1. Water Testing

• Detect and quantify coliforms and enteric pathogens in drinking water, wastewater, and environmental samples.

2. Food and Dairy Testing

• Isolate coliforms and enteric pathogens from dairy products and food matrices.

3. Clinical Diagnostics

• Identify bacterial pathogens from urine, fecal matter, and wound swabs in clinical settings.

4. Research and Surveillance

• Monitor bacterial contamination and resistance trends in environmental and clinical isolates.

Advantages

1. Versatile Diagnostic Medium

• Differentiates a wide variety of pathogenic bacteria, making it suitable for diverse applications.

2. Simple and Effective

• Provides clear and distinct colony appearances for easy interpretation.

3. Compatibility

• Can be used in conjunction with non-selective and selective indicator media for a comprehensive bacterial analysis.

4. Standardized Recommendations

• Endorsed by WHO and health authorities, ensuring global applicability and acceptance.

Specifications

How It Works

1. Media Preparation:
   • Rehydrate the dehydrated powder according to the manufacturer’s instructions.
   • Autoclave and pour into sterile Petri dishes.
2. Sample Inoculation:
   • Streak the sample (e.g., water, food, or biological specimen) onto the agar surface.
3. Incubation:
   • Incubate plates at 35–37°C for 18–24 hours under aerobic conditions.
4. Interpretation:
   • Observe colony morphology and color changes:
     • Red colonies: E. coli (lactose fermenters).
     • Pale pink colonies: Staphylococcus spp. (non-lactose fermenters).
     • Green-brown colonies: Pseudomonas aeruginosa.

Complementary Media

• Desoxycholate Citrate Agar: Enhances isolation of Gram-negative bacteria.
• Brilliant Green Agar: Selective for Salmonella spp..
• Blood Agar: Provides a non-selective baseline for broad pathogen growth.
• Bismuth Sulphite Agar: Ideal for isolating Salmonella typhi.

Why Choose Thermo Scientific™ Oxoid™ MacConkey Agar?

• Global Standards: Recommended by WHO and health authorities.
• Ease of Use: Simple preparation and interpretation with clear colony differentiation.
• Versatility: Suitable for clinical, environmental, and food microbiology.
• Reliable Performance: Consistent results for pathogen isolation and identification.

The Thermo Scientific™ Oxoid™ MacConkey Agar is a trusted, multi-purpose medium that simplifies pathogen detection and differentiation in a variety of settings.

Composition of Thermo Scientific™ Oxoid™ MacConkey Agar (Dehydrated)

The following is the typical formula for MacConkey Agar per liter of prepared medium:

Differences Among MacConkey Agar Variants

MacConkey Agar has several modified formulations, each tailored for specific microbiological applications. These variants differ in their composition, selectivity, and intended use. Below is a detailed comparison of the major MacConkey Agar types:

1. Standard MacConkey Agar

• Purpose: General-purpose medium for the detection and differentiation of lactose-fermenting and non-lactose-fermenting Gram-negative bacteria.
• Selectivity:
  • Selective for Gram-negative bacteria.
  • Inhibits most Gram-positive organisms using bile salts and crystal violet.
• Key Features:
  • Differentiates lactose fermenters (pink colonies) from non-lactose fermenters (colorless colonies).
  • Commonly used for clinical and food microbiology.
• Applications:
  • Isolation of Escherichia coli and other coliforms from clinical and environmental samples.

2. MacConkey Agar No. 2

• Purpose: Specifically designed for the detection of enterococci in the presence of coliforms and non-lactose fermenters.
• Selectivity:
  • Enhanced selectivity for enterococci using Oxoid Bile Salts No. 2 and crystal violet.
  • Inhibits non-fecal streptococci and bile-tolerant Gram-positive cocci.
• Key Features:
  • Enterococci appear as small, intensely red colonies with pale periphery.
  • Non-lactose fermenters appear colorless.
• Applications:
  • Monitoring water, sewage, and food products for fecal contamination.

3. MacConkey Agar No. 3

• Purpose: Optimized for detecting and enumerating coliform organisms, while isolating Salmonella and Shigella species in food, water, and clinical samples.
• Selectivity:
  • Incorporates Oxoid Bile Salts No. 3 and crystal violet for improved selectivity.
  • Completely inhibits Gram-positive cocci.
• Key Features:
  • E. coli: Red colonies with bile precipitation.
  • Salmonella and Shigella: Straw-colored colonies.
  • Recommended by the APHA for food and water testing.
• Applications:
  • Pathogen detection in food (e.g., cheese) and environmental samples.

4. Sorbitol MacConkey Agar (SMAC)

• Purpose: Differentiation of E. coli O157, which does not ferment sorbitol.
• Selectivity:
  • Replaces lactose with sorbitol as the carbohydrate source.
  • Differentiates sorbitol-negative E. coli O157(colorless colonies) from other E. coli strains (pink colonies).
• Key Features:
  • Essential for detecting pathogenic E. coli in food and clinical samples.
• Applications:
  • Food safety testing for shiga toxin-producing E. coli (STEC).
  • Diagnostic testing for E. coli O157in fecal samples.

5. MacConkey Agar with MUG

• Purpose: Detects E. coli using the fluorescence of *MUG (4-Methylumbelliferyl-β-D-glucuronide) under UV light.
• Selectivity:
  • Contains MUG as an indicator for β-glucuronidase activity.
• Key Features:
  • E. coli fluoresces under UV light due to enzymatic activity.
  • Combines lactose differentiation with enzymatic detection.
• Applications:
  • Rapid identification of E. coli in clinical and environmental microbiology.

6. Crystal Violet MacConkey Agar

• Purpose: Enhances selectivity for coliforms by including a higher concentration of crystal violet.
• Selectivity:
  • Strong inhibition of Gram-positive organisms.
• Key Features:
  • Similar to standard MacConkey Agar but with increased inhibition of Gram-positive bacteria.
• Applications:
  • Used in highly contaminated samples to minimize Gram-positive interference.

Key Differences Summary

Conclusion

Each MacConkey variant is optimized for specific applications:

• Standard MacConkey Agar: General-purpose use.
• MacConkey Agar No. 2: Enhanced for enterococci detection.
• MacConkey Agar No. 3: Improved differentiation for Salmonella and Shigella.
• Sorbitol MacConkey Agar (SMAC): Essential for detecting E. coli O157.
• MacConkey with MUG: Combines enzymatic activity detection with traditional differentiation.

Selecting the appropriate variant depends on the target organism and sample type, ensuring accurate and efficient diagnostics.