Thermo Scientific™ Oxoid™ MacConkey Agar No. 2 (Dehydrated)

Thermo Scientific™ Oxoid™ MacConkey Agar No. 2 is a modified version of the traditional MacConkey medium, designed specifically for the detection, enumeration, and differentiation of enterococci, coliforms, and non-lactose fermenters in water, sewage, food products, and other environmental samples. It is a selective medium that inhibits bile-tolerant Gram-positive cocci while allowing enterococci and other indicator organisms to grow, making it ideal for assessing food safety, spoilage, and water quality.

Key Features

1. Selectivity

• Enhanced Selectivity:
  • Utilizes Oxoid Bile Salts No. 2 and crystal violet to inhibit bile-tolerant Gram-positive cocci (e.g., staphylococci) and non-fecal streptococci.
  • Supports the selective growth of enterococci and coliforms.

2. Clear Colony Differentiation

• Enterococci:
  • Appear as small, intensely red colonies with a pale periphery.
• Non-Lactose Fermenters:
  • Appear colorless, allowing easy differentiation.
• Lactose Fermenters:
  • Coliforms (e.g., E. coli) appear red/pink.

3. Versatility

• Suitable for a wide range of sample types, including:
  • Water and wastewater (monitoring pollution and contamination).
  • Dairy products (evaluating spoilage and quality).
  • Food products (testing for hygiene and safety).

4. Optimized Formula

• Incorporates Oxoid Bile Salts No. 2 and crystal violet for improved recognition of enterococci.

Composition (Typical Formula per Liter)

Applications

1. Water and Wastewater Testing

• Detect and quantify enterococci and coliforms as indicators of fecal contamination and water safety.

2. Food and Dairy Analysis

• Monitor spoilage and food safety by identifying coliform organisms and enterococci in food products and dairy samples.

3. Environmental Monitoring

• Evaluate sewage and effluent water for potential public health risks by enumerating fecal indicator organisms.

4. Quality Assurance

• Assess hygiene standards in the food and beverage industry.

Advantages

1. Improved Selectivity

• Enhanced selectivity for enterococci with minimal interference from other Gram-positive cocci.

2. Easy Colony Differentiation

• Provides distinct colony appearances for enterococci, coliforms, and non-lactose fermenters.

3. Versatile Applications

• Suitable for various industries, including food safety, water testing, and environmental monitoring.

4. Reliable and Reproducible

• Manufactured under strict quality control, ensuring consistent results across batches.

How It Works

1. Preparation:
   • Rehydrate the dehydrated powder with distilled water as per the manufacturer's instructions.
   • Autoclave and pour into sterile Petri dishes.
2. Inoculation:
   • Streak the sample (e.g., water, food, or environmental specimen) onto the agar surface.
3. Incubation:
   • Incubate at 35–37°C for 18–24 hours under aerobic conditions.
4. Interpretation:
   • Observe colony morphology:
     • Enterococci: Small, intensely red colonies with pale periphery.
     • Non-lactose fermenters: Colorless colonies.
     • Lactose fermenters (e.g., coliforms): Red/pink colonies.

Complementary Media

• MacConkey Agar No. 1: For general coliform detection.
• MacConkey Agar No. 3: Enhanced bile tolerance for environmental testing.
• Brilliant Green Bile (2%) Broth: For coliform confirmation in food and water samples.
• Blood Agar: Non-selective medium for broad pathogen isolation.

Why Choose MacConkey Agar No. 2?

• Enhanced Selectivity: Ideal for isolating enterococci in mixed cultures.
• Clear Differentiation: Provides precise and distinct colony appearances for easier interpretation.
• Wide Applicability: Suitable for food, water, and environmental testing.
• Reliable Performance: Backed by Thermo Scientific™ quality assurance for consistent results.

The Thermo Scientific™ Oxoid™ MacConkey Agar No. 2 (Dehydrated) is an advanced, selective medium tailored for detecting and enumerating enterococci and coliforms in diverse sample types.

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.