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Dehydrated Culture Media

HALF-FRASER BROTH (WITHOUT FERRIC AMMONIUM CITRATE

Code: CM1053

Half Fraser enrichment medium without ferric ammonium citrate for the isolation of Listeria spp. from food and environmental specimens

Typical Formula*

gm/litre

Proteose peptone

5.0

Tryptone

5.0

"Lab-Lemco" powder

5.0

Yeast extract

5.0

Sodium chloride

20.0

Di-sodium hydrogen phosphate

12.0

Potassium dihydrogen phosphate

1.35

Aesculin

1.0

Lithium chloride

3.0

Nalidixic acid

0.01

Acriflavine hydrochloride

0.0125

pH 7.2 ± 0.2 @ 25°C

 

* Adjusted as required to meet performance standards

Directions

Dissolve 57.4g in 1 litre of distilled water. Mix well and distribute into final containers. Sterilize by autoclaving at 121°C for 15 minutes.
If the addition of ferric ammonium citrate is required, cool to 50°C and add 10ml of a 5% w/v solution prepared in the following way; dissolve 5g of ferric ammonium citrate in 100ml of distilled water and filter sterilize through a 0.2µm filter.

Description
The medium is intended for the isolation of Listeria spp. from food and environmental samples when used as the secondary enrichment medium in methodology for Listeria isolation. It is generally accepted that the USDA-FSIS two stage enrichment method employing UVM primary and secondary enrichment broths is the most suitable for the examination of meat products. Half Fraser Broth is a modification of Fraser Broth which contains half of the concentration of nalidixic acid and acriflavine hydrochloride to aid in the recovery of stressed cells. Half Fraser Broth is used as the primary enrichment broth in the ISO methodology for the detection of Listeria. The removal of ferric ammonium citrate from the formula aids in subculture from the broth to imaging instrumentation or Polymerise Chain Reaction (PCR) based assay machines.

Technique
1. Inoculate 10ml of Half Fraser Broth without FAC with 0.1ml of the primary enrichment broth which has been incubated for 20 to 24 hours.
2. Incubate at 35°C for 26 ± 2 hours in aerobic conditions

Storage instructions
Store the dehydrated medium at 10–30°C and use before the expiry date

 

Appearance
Dehydrated medium: Straw colour, free-flowing powder

Quality control

Control organism:

Expected results

Listeria monocytogenes ATCC® 7644*

3 log increase

Listeria monocytogenes ATCC® 1393

3 log increase

Bacillus cereus ATCC® 10876

No growth

Enterococcus faecalis ATCC® 29212*

No growth

Escherichia coli ATCC® 25922*

No growth

* This organism is available as a Thermo Scientific Culti-Loop® Quality Control Organism

Precautions
Removal of the ferric ammonium citrate from the Half fraser formula means that this product will not turn a dark brown to black colour in the presence of Listeria species.

This medium, with the correct level of ferric ammonium citrate added, complies with standard Half Fraser formulations.

 
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