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Competitive exclusion bacteria control Listeria.

Controlling L. monocytogenes in processing facilities has been a formidable challenge. Floor drains in particular are an important harborage for Listeria. Listeriae can become entrapped on drain surfaces in slimy, protective biofilms.

From floor drains, scientists at the University of Georgia obtained competitive exclusion bacteria (CEB), including L. lactis subsp. lactis (#C-1-92) and E. durans (#152), that inhibit the growth of L. monocytogenes in biofilms at from 4 C to 37 C. Past research indicated that both of these CEB greatly reduce the number of Listeria in floor drains at temperatures from 2 C to 30 C.

Georgia scientists selected a ready-to-eat poultry product processing facility to verify the usefulness of CEB in reducing or eliminating Listeria in floor drains. Seventeen drains in four different locations in the plant were selected for initial screening, and various sites in each drain were analyzed. These included: the inside surface of the drain's cover; the outer surface of the drain basket; sides at the top of the drain; and sides at 5 inches within the drain.

Investigators sampled the drains three times before treating them to determine which drains were consistently Listeria-positive. Researchers found that seven drains were positive at all three sampling times, and two were positive twice. Listeria counts in all positive floor drains were low, with a maximum of 100 Listeria per [cm.sup.2]. Most were Listeria-positive only by selective enrichment culture.

Six of the seven floor drains that were consistently Listeria-positive were selected for CEB treatment. Two drains that were Listeria-positive in two out of three samplings served as controls. They did not receive any CEB treatment. The CEB suspension used to treat the drains contained 25 ml of L. lactis subsp. lactis (#C-1-92) and E. durans (#152) at 109 CFU per ml, as well as 20 ml each of two foaming agents and 1 gal of water. The researchers applied the CEB as a foam 10 times, with the first four treatments applied daily, then twice weekly for three more weeks.

CEB substantially reduced or eliminated Listeria from all of the treated drains. Untreated control drains were consistently positive for Listeria. The treatment appears to control Listeria in most drains for up to eight weeks following the last application. Results suggest the CEB should be applied to drains every two months to control the bacteria.

Further information. Michael Doyle, Center for Food Safety, University of Georgia, Griffin Campus, Melton Building, Griffin, GA 30223; phone: 770-228-7284; fax: 770-229-3216; email:
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Publication:Microbial Update International
Date:Jun 1, 2006
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