Liofilchem® MacConkey Agar w/o Salt

Liofilchem® MacConkey Agar Without Salt is a selective and differential medium designed for the isolation and differentiation of Enterobacteriaceae, staphylococci, and enterococci from clinical specimens, particularly urine. The removal of sodium chloride (NaCl) and crystal violet inhibits the swarming of Proteus spp. and permits the growth of Gram-positive organisms such as Staphylococcus and Enterococcus spp.

Key Features

1. Salt-Free Formulation:
   • Exclusion of sodium chloride prevents the swarming behavior of Proteus spp. while supporting the growth of Gram-positive bacteria.
2. Enhanced Versatility:
   • Absence of crystal violet reduces selectivity, allowing the growth of staphylococci and enterococci alongside coliforms and enteric pathogens.
3. Differential Medium:
   • Lactose fermentation produces a distinct color change, enabling the differentiation of lactose fermenters and non-fermenters.
4. Target Applications:
   • Particularly recommended for urine samples in clinical diagnostics.

Composition (Typical Formula)

Applications

1. Clinical Microbiology:
   • Isolation of coliforms, Proteus spp., Staphylococcus spp., and Enterococcus spp. from urine and other clinical specimens.
   • Differentiation of enteric pathogens in diagnostic workflows.
2. Food and Water Testing:
   • Monitoring for fecal contamination through coliform detection.
   • Identification of enterococci as hygiene indicators.

Preparation Instructions

Dehydrated Medium:

1. Suspend 47.1 g of powder in 1 L of distilled or deionized water.
2. Heat to boiling with frequent agitation until completely dissolved.
3. Sterilize in an autoclave at 121°C for 15 minutes.

Test Procedure

1. Inoculate the agar by directly streaking the specimen on the surface.
2. Incubate plates aerobically at 35 ± 2°C for 18–24 hours.

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

1. Reduced Selectivity:
   • Absence of sodium chloride and crystal violet permits the growth of certain Gram-positive organisms, potentially complicating the differentiation of Gram-negative bacteria.
2. Presumptive Identification:
   • Colonial appearance provides presumptive identification; confirmatory tests (e.g., biochemical assays) are required for definitive results.
3. Specimen Quality:
   • Improper sample collection or storage may affect the growth and results.

Advantages

1. Inhibits Swarming:
   • Prevents the swarming of Proteus spp., making colony isolation more manageable.
2. Broader Utility:
   • Supports the growth of Gram-positive organisms such as staphylococci and enterococci, enhancing its versatility for mixed flora specimens.
3. Optimized for Urine Analysis:
   • Particularly suitable for isolating pathogens from urinary tract infections.

Liofilchem® MacConkey Agar Without Salt is a versatile medium for isolating enteric bacteria, staphylococci, and enterococci in urine and other clinical specimens. Its salt-free formulation improves usability for specific applications by inhibiting Proteus spp. swarming while promoting Gram-positive growth. This makes it an essential tool for diagnostic microbiology laboratories focused on urinary tract and mixed-flora infections.