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LISTERIA ENRICHMENT BROTH BASE

Code: CM0862

LISTERIA SELECTIVE ENRICHMENT SUPPLEMENT

Code: SR0141

Directions
Suspend 18g in 500ml of distilled water. Add the contents of one vial of Listeria Selective Enrichment Supplement (SR0141), reconstituted with 2ml of distilled water. Sterilize by autoclaving at 121°C for 15 minutes. Cool to 50°C, mix well and distribute into sterile containers in volumes as required.

LISTERIA SELECTIVE ENRICHMENT SUPPLEMENT (modified with 10 mg/litre of Acriflavine)

Code: SR0149.

Directions
Aseptically add 10ml of distilled water to one vial and invert gently to dissolve. Add the vial contents to 2.25 litres of Listeria Enrichment Broth Base. Sterilize by autoclaving at 121°C for 15 minutes. Cool to 50°C, mix well and distribute into sterile containers in volumes as required .

Description
Listeria Selective Enrichment Medium is based on the formulation described by Lovett et al.¹ and is recommended for the selective enrichment of Listeria species from food. The enrichment procedure has been shown to recover an inoculum of less than 10 cfu/ml from raw milk.

In order to achieve a higher isolation rate it is recommended that the enrichment broth is subcultured onto Listeria Selective Agar plates after 1, 2 and 7 days. Agello et al.², have shown that extending the incubation period to 7 days allows better recovery of environmentally stressed listeria from milk and milk products.

Technique
1. Add 25g or 25ml samples to 225ml of Listeria Selective Enrichment Broth. Homogenise if required.
2. Incubate at 30°C for 7 days.
3. Subculture from the Listeria Selective Enrichment Broth onto Listeria Selective Agar plates (see Note) after 1, 2 and 7 days by:
(i) Direct plating onto Listeria Selective Agar plates.
(ii) Adding 1ml of the Listeria Selective 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
Store the dehydrated medium at 10-30°C and use before the expiry date on the label.
Store the prepared medium at 2-8°C.

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

Quality control

* This organism is available as a Culti-Loop®

Precautions
Note the precautions stated under Listeria Selective Medium (Oxford) CM0856 and SR0140. Broth cultures are more dangerous than colonies on agar plates.
Store prepared medium away from light. Acriflavine can photo-oxidise to form inhibitory compounds against Listeria.
Supplement SR0141 used in this medium contains a toxic concentration of cycloheximide. Note the precautions to be taken under HAZARDS.

References
1. Lovett J., Francis D. W. and Hunt J. M. (1987) Journal of Food Protection 50. 188-192.
2. Agello G., Hayes P. and Feeley J. (1986) Abstracts of the Annual Meeting, ASM, Washington DC p5.