IMPROVED ISOLATION OF LISTERIA SPP
IDG has introduced a new selective medium under its LAB M brand for improved
isolation of Listeria spp. Utilising a novel specific substrate for the
detection of glucosidase activity, Harlequin" Listeria medium has proved
superior to Oxford formulations, with significantly improved isolation rates
(34%) and clearer differentiation of colonies.
Listeria spp. have again been implicated in a number of high profile cases
of food poisoning, leading to the recall of a wide range of contaminated
products. The risk to health from infection can be very serious, with
symptoms covering the full spectrum from a flu-like illness and diarrhoea,
to meningitis, septicaemia and death. The financial implications for the
food industry of an outbreak or product recall are also severe, increasing
the need for comprehensive product testing.
Harlequin " Listeria Medium offers a simple and effective plating system,
introducing significant benefits to the microbiologist. Confidence in
testing is improved; positives can be detected earlier and with easy
identification of colonies, plates can be screened faster. The medium
utilises the same selective antibiotic supplement as the Oxford formulation,
but the incorporation of a specific chromogen, CHE-glucoside, is
incorporated to detect b-glucosidase. Cleaving of the substrate releases an
insoluble black pigment that is retained within the colony, unlike Oxford
medium where it diffuses into the surrounding medium.
The intense black coloration against a clear agar, makes screening for
suspect colonies very easy and a reduced concentration of antibiotic
improves recovery. In a recent study, the isolation rates of Oxford
formulation and the new medium were compared.
Harlequin " Listeria Medium gave a 34% increase in the isolation of Listeria
spp. with 85% of positives detectable after 22 hrs incubation.
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Editor: For more information, please contact: Phil Smith, IDG UK Ltd, Topley
House, 52 Wash Lane, Bury, Lancs, BL9 6AU, Phone: 0161 797 5729, Fax: 0161
762 9322
Email: pasmith at idgplc.com
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Damian Bond
Tel 0161 236 7816
Mobile 0498 600 833
e-mail damian.bond at virgin.net
