Liofilchem® Listeria Oxford Agar

Listeria Oxford Agar is a selective and differential culture medium designed for the isolation and presumptive identification of Listeria species, particularly Listeria monocytogenes, from foods, milk and dairy products, clinical specimens, and environmental samples, in accordance with ISO 10560.

The medium is supplied as a dehydrated agar containing selective agents and requires the addition of Listeria Oxford Supplement to achieve full selectivity against competing microorganisms.

Principle of the Medium

Listeria Oxford Agar combines nutrient-rich components with selective and differential agents to support the growth of Listeria spp. while inhibiting background flora:

• Peptospecial, peptone, and tryptose provide amino acids, nitrogen, and growth factors.
• Maize starch protects Listeria cells from toxic metabolites.
• Sodium chloride maintains osmotic balance.
• Lithium chloride, cycloheximide, and acriflavine contribute to selectivity by inhibiting competing bacteria and fungi.
• Colistin sulphate, phosphomycin, and cefotetan (added via Oxford Supplement) suppress Gram-negative and contaminating bacteria.
• Esculin and ferric ammonium citrate enable differentiation: Listeria spp. hydrolyze esculin to esculetin, which reacts with ferric ions to produce black or dark brown colonies with halos.
• Agar acts as the solidifying agent.

Typical Colony Morphology

• Listeria spp.: Grey-brown colonies surrounded by a brown to black halo
• Listeria monocytogenes: Convex grey colonies with a distinct black halo

Suspect colonies should be confirmed using Gram staining, biochemical identification, hemolysis testing on Columbia Agar with 5% sheep blood, and CAMP tests.

Preparation

1. Suspend 60.9 g of dehydrated medium in 1 liter of distilled or deionized water.
2. Heat until completely dissolved.
3. Autoclave at 121 °C for 15 minutes.
4. Cool to 45–50 °C.
5. Aseptically add 2 vials of Listeria Oxford Supplement (code 81027), each reconstituted with 5 mL sterile distilled water.
6. Mix well and pour into sterile Petri dishes.

Applications

• Detection of Listeria spp. in food and dairy products
• Environmental monitoring in food processing facilities
• Clinical and public health microbiology
• Quality control and regulatory food safety testing

Quality Control Performance

Product Specifications

• Final pH: 7.0 ± 0.2 at 25 °C
• Dehydrated Medium Appearance: Free-flowing, beige powder
• Prepared Medium Appearance: Clear, dark amber
• Incubation: 36 ± 1 °C for 24–48 hours
• Shelf Life: As indicated on label

Storage

• Store dehydrated powder at 10–30 °C in a dry environment, tightly closed.
• Store prepared plates at 2–8 °C.
• Do not use if signs of deterioration or contamination are observed.

Packaging & Ordering Information

Standards & References

• ISO 10560: Detection of Listeria monocytogenes in milk and milk products
• TIL-IDF (1988): Recommended methods for Listeria detection

Liofilchem® Listeria Oxford Agar is a proven, selective, and differential medium for reliable isolation of Listeria spp. from complex samples. Its compatibility with ISO-recognized methods and clear colony differentiation make it an essential tool for food safety, environmental monitoring, and public health microbiology laboratories.