This medium is a modification of the full-strength Fraser Broth, containing half the concentration of selective agents (Nalidixic acid and Acriflavine) to allow for the recovery of stressed or sublethally injured Listeria cells often found in processed foods. The base contains Proteose Peptone, Tryptone, and Beef Extract to provide nitrogen and vitamins, while Yeast Extract offers essential B-complex vitamins. Lithium Chloride and the reduced-strength antibiotic supplement inhibit the growth of competitive microflora like Enterococci and Gram-negative bacteria. The medium also acts as a differential indicator: Listeria spp. hydrolyze Esculin to esculetin, which reacts with Ferric Ammonium Citrate (added separately) to produce a blackening of the broth, signaling a presumptive positive result.
Advantages
- ISO Standard Compliance: Specifically designed to meet the requirements of ISO 11290 for the primary enrichment phase.
- Optimized Recovery: The "Half-strength" selective formula is gentler on damaged Listeria cells, ensuring higher detection rates in complex matrices.
- High Selectivity: Effectively suppresses background flora even at reduced antibiotic concentrations due to the synergistic effect of Lithium Chloride.
- Visual Presumptive Indicator: The blackening of the broth provides an early visual indication of the presence of Listeria.
- Reliable Base: Provides a stable nutrient environment for the transition to secondary enrichment in full-strength Fraser Broth.
Technical specifications
| Catalogue number |
1183 |
| Brand |
Condalab |
| Application |
Primary enrichment of Listeria monocytogenes (ISO 11290) |
| Typical Composition (g/L) |
Proteose Peptone (5.0); Tryptone (5.0); Beef Extract (5.0); Yeast Extract (5.0); Sodium Chloride (20.0); Lithium Chloride (3.0); Esculin (1.0); Disodium Phosphate (12.0); Monopotassium Phosphate (1.35) |
| Final pH (at 25 °C) |
7.2 ± 0.2 |
| Preparation |
57.4 g/L (Add Half-Fraser + Ferric Citrate Supplements) |
| Storage Temperature |
2 – 25 °C |
Available packaging options
| 1183 |
500 g plastic bottle |
