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Culture Media Supplements

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FRASER BROTH BASE

Code: CM0895

A secondary selective diagnostic enrichment medium 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

pH 7.2 ± 0.2 @ 25°C

 
*  Adjusted as required to meet performance standards
 † unchanged by addition of supplements

FRASER SUPPLEMENT

Code: SR0156

Vial contents (each vial is sufficient for 500ml of medium)

per vial
per litre

Ferric ammonium citrate

0.25g

0.5g

Nalidixic acid

10.0mg

20.0mg

Acriflavine hydrochloride

12.5mg

25.0mg

Directions
Suspend 28.7g in 500ml of distilled water and mix well to dissolve completely. Sterilise by autoclaving at 121°C for 15 minutes. Cool to below 50°C, and aseptically add the contents of one vial of Fraser Selective Supplement (SR0156) reconstituted as directed in the product insert. Mix well and distribute into sterile containers.

HALF FRASER SUPPLEMENT

Code: SR0166

A selective supplement for the primary enrichment of Listeria spp. from food and environmental samples when used with Fraser Broth

Vial contents

SR0166E
per vial 
SR0166G
per vial
per litre
(before sample addition)

Ferric ammonium citrate

112.5mg

1.125g

500mg

Nalidixic acid

2.25mg  

22.5mg

10.0mg

Acriflavine hydrochloride

2.8125mg 

 28.125mg

12.5mg

Directions
Suspend 12.9g of Fraser Broth in 225ml of distilled water., and mix well to dissolve completely Sterilise by autoclaving at 121°C for 15 minutes. Cool to below 50°C, and aseptically add the contents of one vial of Half Fraser Selective Supplement SR0166E reconstituted as directed in the product insert. Mix well and distribute into sterile containers. Alternatively, to make 2.25 litres, use 129.0g of CM0895 and 1 vial of SR0166G.

Description
Fraser Broth is a modification of the USDA-FSIS (United States Department of Agriculture-Food Safety Inspection Service) UVM secondary enrichment broth and is based on the formula described by Fraser and Sperber1. It contains ferric ammonium citrate and lithium chloride. Blackening of the medium is presumptive evidence of the presence of Listeria. Contrary to early indications, cultures which do not blacken cannot be assumed to be Listeria-free. All Fraser Broth enrichment cultures should be subcultured to plating medium.

The medium is intended for the isolation of Listeria spp. from food and environmental samples when used as the secondary enrichment medium in the USDA-FSIS 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. Fraser Broth has proven to be remarkably accurate in detecting Listeria spp. in food and environmental samples1,2.

All Listeria spp. hydrolyse aesculin to aesculetin. Aesculetin reacts with ferric ions which results in blackening. Another possible advantage to the addition of ferric ammonium citrate is that it has been shown that ferric ions enhance the growth of Listeria monocytogenes3. Lithium chloride is included in the medium to inhibit the growth of enterococci which can also hydrolyse aesculin. Care must be taken when using Fraser Broth with DNA probe methodology because the high salt content of the medium may have an inhibitory effect on detection4.

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 methodology5 for the detection of Listeria.

Technique
1. Inoculate 10ml of Fraser Broth with 0.1ml of the primary enrichment broth (i.e. FDA or UVM I enrichment broth) which has been incubated for 20 to 24 hours.
2. Incubate at 35°C for 26 ± 2 hours in air.
3. Compare each inoculated tube to an inoculated control against a white background. Tubes that darken or turn black should be subcultured on to Oxford Medium or PALCAM Medium. Tubes that retain the original yellow colour should also be inoculated on plating media and confirmed as free from Listeria spp. before discarding.

N.B. Fraser Medium should be incubated for 26 ± 2 hours to ensure at least 24 hours incubation period to permit the development of the black colour.

Storage conditions and Shelf life
Store the dehydrated medium at 10-30°C and use before the expiry date on the label.
Store the selective supplement in the dark at 2-8°C and use before the expiry date on the label.
The prepared medium may be stored for up to 2 weeks at 2-8°C.

Appearance
Dehydrated medium: Straw coloured, free-flowing powder
Prepared medium: Straw coloured solution

Quality control
(Fraser Broth and Half Fraser Broth)

Positive control:

Expected results

Listeria monocytogenes ATCC® 7466*

Blackening

Negative control:

 
Psudomonas aeruginosa ATCC® 27853*No blackening
* This organism is available as a Culti-Loop®

References
1. Fraser J.A. and Sperber W.H. (1988) J. Food Protect. 51, No.10, 762-765.
2. McClain D. and Lee W.H. (1988) J. Assoc. Off. Anal. Chem. 71, NO.3, 660-664.
3. Cowart R.E. and Foster B.G. (1985) J. Infect. Dis. 151, 721-730.
4. Partis L., Newton K., Marby J. and Wells R.J. (1994) Appl. Env. Microbiol. 60, 1693-1694.
5. Microbiology of Food and Animal Feeding Stuffs - Horizontal method for the detection and enumeration of Listeria monocytogenes Part. 1: Detection Method BS EN ISO 11290:1 1997.

 
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