Liofilchem® MacConkey Agar w/o Crystal Violet

Liofilchem® MacConkey Agar Without Crystal Violet is a selective and differential medium designed for isolating and differentiating enteric organisms from various clinical, food, and environmental samples. The absence of crystal violet makes the medium less selective, allowing the growth of staphylococci, enterococci, and even Mycobacterium spp., alongside Gram-negative bacteria.

Key Features

1. Selective Growth:
   • No Crystal Violet: Reduced selectivity to permit the growth of Gram-positive organisms such as enterococci and staphylococci, along with coliforms and other Gram-negative bacteria.
   • Bile Salts: Retains selective properties to inhibit most Gram-positive bacteria, except enterococci and staphylococci.
2. Differentiation of Lactose Fermenters:
   • Lactose-fermenting bacteria (e.g., E. coli, Klebsiella spp.) produce pink to red colonies.
   • Non-lactose fermenters (e.g., Salmonella spp., Proteus spp.) form colorless colonies.
3. Extended Utility:
   • Permits growth of certain Mycobacterium spp., particularly the potentially pathogenic Mycobacterium fortuitum-chelonae complex.

Applications

1. Clinical Microbiology:
   • Isolating enteric pathogens from fecal, urine, and other clinical specimens.
   • Detecting coliforms in cases of suspected enteric infections.
2. Food and Environmental Testing:
   • Monitoring coliforms and enteric pathogens in foodstuffs and wastewater.
   • Identifying fecal contamination in water samples.
3. Research Use:
   • Suitable for studying the behavior of mixed microbial flora, including Gram-positive organisms like staphylococci and enterococci.

Composition (Typical Formula)

Preparation Instructions

For Dehydrated Medium:

1. Suspend 50 g of the powder in 1 L of distilled or deionized water.
2. Heat to boiling, stirring frequently until completely dissolved.
3. Autoclave at 121°C for 15 minutes.
4. Cool to 45–50°C, mix well, and pour into sterile Petri dishes.

Test Procedure

1. Inoculate the plate by streaking the specimen directly onto the agar surface.
2. Incubate aerobically at 35 ± 2°C for 18–72 hours.
3. Adjust incubation time and temperature based on specific applications.

Interpreting Results

Appearance

Storage and Shelf Life

• Dehydrated Medium: Store at 10–30°C in a dry, tightly sealed container. Shelf life: 4 years.
• Prepared Plates: Store at 10–25°C away from light. Shelf life: 6 months.

Quality Control

Limitations

• The absence of crystal violet reduces selectivity, allowing some Gram-positive organisms to grow.
• Further biochemical or serological tests are needed for definitive identification.
• Growth may vary for organisms with specific nutritional or environmental requirements.

Applications in Context

1. Clinical Use:
   • Identification of coliforms and potential pathogens in fecal or urinary infections.
2. Food and Water Testing:
   • Monitoring hygiene and detecting fecal contamination.
3. Research:
   • Studying the growth dynamics of mixed microbial populations, including staphylococci and enterococci.

Liofilchem® MacConkey Agar Without Crystal Violet is a versatile medium suitable for isolating enteric pathogens while accommodating the growth of certain Gram-positive organisms. Its applications in clinical diagnostics, food safety, and environmental monitoring make it a valuable tool for microbiology laboratories.