Half-Fraser broth is a selective enrichment broth for the identification and isolation of Listeria spp., primarily from food and environmental samples.
The antibiotics, nalidixic acid and acriflavine, are already included in the formulation so only ferric ammonium citrate (LS5004) need be added to make the complete Half-Fraser broth.
The peptones provide carbon, nitrogen and vitamins, sodium chloride provides osmotic balance and the phosphate buffer system maintains pH.
Lithium chloride inhibits enterococci and the antibiotics make the medium highly selective.
Listeria spp. hydrolyse aesculin to aesculetin which forms a confirmatory dark brown or black complex with Fe3+ ions.
Fraser Half-Broth Strength
Additional Information
| Shelf Life (days) | |
|---|---|
| Storage Temp (°C) | |
| Dehydrated Medium Appearance | |
| Prepared Medium Appearance | |
| Dehydrated Medium Colour | |
| Prepared Medium Colour | |
| Dehydrated PH | |
| Prepared PH | |
| Recommended Incubation | |
| Container |
Product Description
| Organism | Ref. No. | Result |
|---|---|---|
| Listeria monocytogenes | NCTC 11994 | Turbid growth |
| Listeria innocua | NCTC 11288 | Turbid growth |
| Escherichia coli | NCTC 12241 | No growth |
| Enterococcus faecalis | NCTC 12697 | No growth |
Formula*
| FORMULA* | g/L |
|---|---|
| Enzymatic digest of animal tissue | 5 |
| Enzymatic digest of casein | 5 |
| Meat extract | 5 |
| Yeast extract | 5 |
| Sodium chloride | 20 |
| Di-sodium hydrogen phosphate | 9.6 |
| Potassium dihydrogen phosphate | 1.35 |
| Aesculin | 1 |
| Lithium chloride | 3 |
| Nalidixic acid | 0.01 |
| Acriflavin | 0.0125 |
| Total | 55 |
Preparation
Suspend 55.0 g of the medium in one litre of deionised / purified water. Allow the medium to soak whilst mixing for 10 minutes.
Sterilise at 121°C for 15 minutes with frequent stirring to completely dissolve the medium. Cool to 42-46°C. To make Half-Fraser broth add 2 vials of LS5004 or to make Fraser broth add 2 vials of LS5003. Mix well and dispense into appropriate sterile containers