Liofilchem® MacConkey Agar No. 2

Liofilchem® MacConkey Agar No. 2 is a selective medium designed specifically for the isolation and differentiation of enterococci in mixed microbial populations, such as those found in water, food, and clinical specimens. This medium also enables differentiation of Gram-negative enteric bacteria based on their lactose fermentation capabilities.

Intended Purpose

• Detection and identification of enterococci as indicators of fecal contamination.
• Differentiation between lactose-fermenting (e.g., Escherichia coli, Klebsiella spp.) and non-lactose fermenting bacteria (e.g., Salmonella spp., Shigella spp., Proteus spp.).
• Suitable for samples with mixed microbial flora, such as clinical specimens, food samples, and water.

Key Features

1. Enhanced Selectivity:
   • Formulated with Bile Salts No. 2, which are less inhibitory, allowing better growth and recognition of enterococci compared to other MacConkey formulations.
2. Differentiation of Microbial Flora:
   • Lactose-fermenting bacteria: Produce pink to red colonies due to acid production.
   • Non-lactose fermenting bacteria: Form colorless colonies.
   • Enterococci: Appear as small, intensely colored red colonies surrounded by a pale red precipitate.
3. Wide Application:
   • Suitable for clinical diagnosis, food and water safety testing, and environmental monitoring.
4. Reliable Composition:
   • Complies with performance standards for use in microbiology laboratories.

Composition (Typical Formula)

Applications

1. Clinical Microbiology:
   • Used to identify Enterococcus faecalis in urine and fecal specimens as an indicator of fecal contamination or infection.
   • Differentiates pathogenic Gram-negative bacteria like Salmonella and Shigella.
2. Food and Water Testing:
   • Detects enterococci in water and food samples as indicators of hygienic quality and fecal contamination.
3. Environmental Monitoring:
   • Identifies enteric pathogens in wastewater and environmental samples.

Preparation Instructions

For Dehydrated Medium:

1. Suspend 50.0 g of the powder in 1 L of distilled or deionized water.
2. Heat to dissolve, boiling for 1 minute with frequent agitation.
3. Sterilize in an autoclave at 121°C for 15 minutes.

Interpretation of Results

Performance Testing

Performance is validated using the following quality control strains:

Storage and Shelf Life

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

Limitations

1. Specific Growth Requirements:
   • Some fastidious strains may exhibit weak or no growth on this medium.
   • Use a non-selective medium like Columbia Agar with 5% sheep blood for parallel testing.
2. Presumptive Identification:
   • Further biochemical or molecular testing is required to confirm bacterial identification.
3. Specimen Quality:
   • Poor specimen collection or handling may lead to invalid results.

Precautions

• For in vitro diagnostic use (IVD) only.
• Operators must be trained in microbiological techniques.
• Handle all clinical specimens and reagents as potentially infectious.
• Dispose of waste according to local and national regulations.

MacConkey Agar is a selective and differential culture medium widely used to isolate and differentiate Gram-negative enteric bacteria based on their ability to ferment lactose. Various manufacturers offer formulations with slight variations to suit specific applications. Below is a comparison of the compositions of MacConkey Agar from different brands:

Notes:

• Peptone: Serves as a source of nitrogen, vitamins, and minerals essential for bacterial growth.
• Lactose: Acts as the fermentable carbohydrate to differentiate lactose fermenters (which produce pink colonies) from non-fermenters (which produce colorless colonies).
• Bile Salts and Crystal Violet: Function as selective agents to inhibit the growth of Gram-positive bacteria, allowing for the selective isolation of Gram-negative organisms.
• Neutral Red: Serves as a pH indicator that turns red in acidic conditions resulting from lactose fermentation.
• Agar: Provides the solidifying agent for the medium.

While the core components are consistent across these brands, slight variations exist in the concentration of peptone and agar, which may influence the medium's performance in specific applications. For instance, BD's formulation includes a slightly lower concentration of peptone (17.0 g/L) compared to others. These differences can affect the growth characteristics and differentiation of certain bacterial species.

When selecting a MacConkey Agar product, it's essential to consider the specific requirements of your laboratory procedures and the bacterial strains of interest. Consulting the technical datasheets provided by each manufacturer can offer further insights into the suitability of their formulations for your applications.

The Liofilchem® MacConkey Agar No. 2 is a reliable selective medium for the isolation of enterococci and differentiation of enteric pathogens in clinical, food, and environmental samples. Its formulation with Bile Salts No. 2 enhances selectivity for enterococci, making it a valuable tool for laboratories involved in diagnostic and safety testing.