Liofilchem® MacConkey Agar with Bile Salts & Crystal Violet

Liofilchem® MacConkey Agar is a selective and differential medium used for the detection and differentiation of Gram-negative enteric bacteria, particularly from samples of clinical, food, environmental, and pharmaceutical origins. It is widely utilized for identifying lactose-fermenting and non-lactose-fermenting organisms such as Escherichia coli, Klebsiella spp., Salmonella spp., and Shigella spp..

Intended Purpose

This medium is designed to:

• Selectively inhibit the growth of Gram-positive bacteria.
• Differentiate Gram-negative enteric bacteria based on their ability to ferment lactose.
• Support diagnostic workflows by providing presumptive identification of pathogens such as E. coli in feces, urine, foodstuffs, wastewater, and non-sterile pharmaceutical products.

It is a valuable diagnostic aid, although additional confirmatory tests are required for definitive results.

Key Features

1. Selective and Differential:
   • Crystal Violet and Bile Salts inhibit Gram-positive organisms, ensuring selective growth of Gram-negative bacteria.
   • Lactose Fermentation is indicated by a color change due to acid production, differentiating lactose fermenters (pink colonies) from non-fermenters (colorless colonies).
2. Wide Range of Applications:
   • Effective for clinical samples (e.g., feces, urine).
   • Supports food and environmental safety testing.
   • Used in pharmaceutical microbiology for detecting E. coli contamination in non-sterile products.
3. Standardized Formula:
   • Complies with harmonized USP/EP/JP methods for microbial testing.
   • Suitable for detecting E. coli and other Enterobacteriaceae from a variety of matrices.
4. High Reliability:
   • Consistent and reproducible results validated by quality control strains, including E. coli (ATCC® 8739), Salmonella Typhimurium (ATCC® 14028), and Shigella flexneri (ATCC® 12022).

Composition (Typical Formula)

Preparation

For Dehydrated Medium:

1. Suspend 51.5 g of powder in 1 L of distilled water.
2. Heat to dissolve completely, boiling for 1 minute with frequent agitation.
3. Autoclave at 121°C for 15 minutes.
4. Cool to 45–50°C and pour into sterile Petri dishes.

For Pre-Bottled Medium:

1. Melt the medium in a water bath at 100°C.
2. Cool to 45–50°C, mix well, and aseptically distribute into Petri dishes.

Applications

1. Clinical Microbiology:
   • Identification of enteric pathogens from fecal, urine, or other biological samples.
   • Presumptive identification of lactose-fermenting bacteria like E. coli.
2. Food Microbiology:
   • Detection of Salmonella and other pathogens in foodstuffs.
3. Environmental Testing:
   • Isolation of E. coli and other Gram-negative bacteria from wastewater.
4. Pharmaceutical Microbiology:
   • Detection of E. coli in non-sterile pharmaceutical products using harmonized methods.

Interpreting Results

Quality Control

Performance Characteristics

• Validated against standard QC strains.
• Reliable in differentiating lactose fermenters from non-fermenters.

Limitations

• May require additional confirmatory tests for definitive identification.
• Growth can vary based on specific organism requirements or environmental factors.

Storage and Shelf Life

• Dehydrated Medium: 4 years at 10–30°C in a dry environment.
• Pre-Bottled Medium: 2 years.
• Prepared Plates: 6 months at 10–25°C away from light.

Safety and Precautions

1. For in vitro diagnostic use only.
2. Handle clinical specimens and reagents as potentially infectious.
3. Dispose of all waste following local and national regulations.
4. Use appropriate personal protective equipment (PPE).

MacConkey Agar is a widely used selective and differential medium designed to isolate and differentiate Gram-negative enteric bacteria based on their lactose fermentation capabilities. Various formulations exist, each tailored for specific applications. Below is a comparative analysis of Liofilchem® MacConkey Agar with Bile Salts & Crystal Violet, Oxoid MacConkey Agar No. 2, Oxoid MacConkey Agar No. 3, and other common brands.

1. Composition

2. Selectivity and Differentiation

3. Applications

4. Key Differences

• Oxoid MacConkey Agar No. 2: Contains a higher concentration of bile salts (5.0 g/L) and lacks crystal violet, making it particularly useful for recognizing enterococci in the presence of coliforms and non-lactose fermenters.
• Oxoid MacConkey Agar No. 3: Incorporates both bile salts and crystal violet, providing enhanced selectivity against Gram-positive bacteria and improved differentiation between coliforms and non-lactose fermenting organisms.
• Liofilchem® MacConkey Agar: Features a balanced composition with both bile salts and crystal violet, suitable for a broad range of applications, including compliance with harmonized USP/EP/JP methods for detecting E. coli in non-sterile pharmaceutical products.

5. Considerations for Selection

• Target Organisms: Choose a formulation based on the specific Gram-negative bacteria of interest and the presence of Gram-positive flora in the sample.
• Sample Type: Consider the origin of the sample (clinical, food, water, pharmaceutical) to select the most appropriate medium.
• Regulatory Compliance: Ensure the medium aligns with relevant standards and guidelines for the intended application.

In summary, while all these MacConkey Agar formulations serve the fundamental purpose of isolating and differentiating Gram-negative enteric bacteria, variations in their composition, particularly concerning bile salts and crystal violet concentrations, influence their selectivity and suitability for specific applications.

Liofilchem® MacConkey Agar is an essential tool in microbiology labs for the isolation and differentiation of Gram-negative enteric bacteria. Its selective and differential properties make it suitable for applications ranging from clinical diagnostics to food and environmental safety testing. With its compliance to USP/EP/JP standards, it ensures reliability and reproducibility across a wide range of testing scenarios.