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Dehydrated Culture Media

BUFFERED LISTERIA ENRICHMENT BROTH

Code: CM0897

A selective enrichment medium for the detection of Listeria monocytogenes when prepared from Buffered Listeria Enrichment Broth base and Listeria Selective Supplement SR0141.

BUFFERED LISTERIA ENRICHMENT BROTH

Typical Formula*

gm/litre

Tryptone soya broth

30.0

Yeast extract

6.0

Potassium di-hydrogen orthophosphate

1.35

Disodium hydrogen orthophosphate

9.60

Final pH 7.3 ± 0.2 @ 25°C

 
* Adjusted as required to meet performance standards

LISTERIA SELECTIVE ENRICHMENT SUPPLEMENT

Code: SR0141

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

per vial
per litre

Nalidixic acid

20.0mg

40.0mg

Cycloheximide

25.0mg

50.0mg

Acriflavine hydrochloride

7.5mg

15.0mg

MODIFIED LISTERIA SELECTIVE ENRICHMENT SUPPLEMENT

Code: SR0213

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

per vial
per litre

Nalidixic acid

20.0mg

40.0mg

Amphotericin B

5.0mg

10.0mg

Acriflavine hydrochloride

7.5mg

15.0mg

Directions
Add 23.5g to 500ml of distilled water and mix well to dissolve. Add the contents of 1 vial of Listeria Selective Enrichment  Supplement SR0141 or the alternative Modified Listeria Selective Supplement SR0213 reconstitued as directed.  Sterilize by autoclaving at 121°C for 15 minutes. Cool to 50°C, mix well and aseptically distribute into sterile containers in volumes as required.

Description
Listeria Selective Enrichment Broth CM0862 is based on the formulation described by Lovett et al.1 and is recommended for the enrichment of Listeria species in food. Subsequent work has concluded that the enrichment properties can be improved by increasing the buffering capacity of the medium by the addition of potassium di-hydrogen orthophosphate and disodium hydrogen orthophosphate. Buffered Listeria Enrichment Broth is therefore a modification of the original medium.

Techniques
1. Add 25g or 25ml samples to 225ml of Buffered Listeria Enrichment Broth. Homogenise if required.
2. Incubate at 30°C for 48 hours.
3. Subculture from the Buffered Listeria Emrichment Broth onto Listeria Selective Agar plates (See Note) after 24 and 48 hours by:
(i) Direct plating onto Listeria Selective Agar plates.
(ii) Adding 1ml of the Buffered Listeria Enrichment Broth to 9ml of 0.5% KOH, vortex mixing, and plating onto Listeria Selective Agar plates.
Note
Suitable Listeria Selective Media are:
1. Listeria Selective Medium (Oxford formulation) (Oxoid CM0856 and Oxoid SR0140).
2. PALCAM Medium (Oxoid CM0877 and Oxoid SR0150)

Storage conditions and Shelf life
Buffered Listeria Enrichment Broth should be stored tightly capped in the original container in a cool, dry place away from bright light. When stored as directed the medium will remain stable until the expiry date printed on the label.

Listeria Selective Enrichment Supplement SR0141 as supplied should be stored at 2-8°C. When stored as directed the reagents are stable until the expiry date printed on the label.

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

Quality control

Positive control:

Expected results

Listeria monocytogenes ATCC® 19117

Turbid growth

Negative control:

 
Enterococcus faecalis ATCC® 29212*

Inhibited

* This organism is available as a Culti-Loop®

Precautions
Listeria Selective Enrichment Supplement contains cycloheximide and is toxic if swallowed, inhaled or by skin contact. As a precaution when handling wear gloves and eye/face protection.
Acriflavine is activated by light and may form compounds inhibitory for Listeria.

References
1. Lovett J., Francis D.W. and Hunt J.M. (1987) J. Food Prot. 50. 188-192.
2. Curtis G.D.W., Nichols W.W. and Falla T.J. (1989) Lett. Appl. Micro. 8. 169-172.

 
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