Listeria Enrichment Broth

LAB 138

Listeria Isolation Medium

(Oxford Formulation)

Description

A medium for the selective enrichment of food and environmental samples for Listeria spp. first described in 1987 by J. Lovett. The medium offers more rapid enrichment than the low temperature enrichment techniques. This medium is now recommended by the Commission of European Communities and the International Dairy Federation for the examination of soft cheeses for Listeria monocytogenes. The medium is incubated at 30˚C and utilises acriflavine, nalidixic acid and cyclohexamide as selective agents.

Method for reconstitution

Weigh 36 grams of powder and add to 1 litre of deionised water. Allow to soak for 10 minutes then swirl to mix and sterilise by autoclaving at 121˚C for 15 minutes. Cool to 47˚C and add 2 vials of X138 (X139/X539 can be used as an alternative) reconstituted in 50% alcohol. Aseptically dispense into sterile tubes or bottles.

Appearance: Yellow, clear.

pH: 7.3 ± 0.2

Minimum Q.C. organisms: L. monocytogenes NCIMB 50007 E. coli (inhibition) NCIMB 50034

Storage of Prepared Medium: Capped containers - up to 14 days at 2-8˚C in the dark.

Inoculation: Add 25 grams of sample to 225mls of Listeria Enrichment Broth and homogenise.

Incubation: 30˚C aerobically for up to 48 hours.

Subculture: After 24 and 48 hours onto Listeria Isolation Medium - LAB 122.

References

Lovett, J. Frances, D.W. Hunt, J.M. J. Food Protect. 50: 188-192. Bolton, F. J. Personal Communication Public Health Laboratory, Preston U.K.