Separation of Listeria from cheese and enrichment media using antibody-coated microbeads and centrifugation

An immunoseparation system for the separation of Listeria from enriched che ese samples was developed. The system utilizes polystyrene microbeads (3.8 mum in diameter) coated with covalently bound anti-Listeria genus-specific antibody. The beads were incubated with cheese enriched in half-Fraser brot h and the bead-bacterial complex was separated by centrifugation at 110g th en spread on selective agar plates. Although cross-reactivity with certain Gram-positive bacteria (Staphylococcus saprophyticus and Arthrobacter sp.) was determined, this had no negative effect on capture effectiveness of the beads to Listeria spp. The minimum density of Listeria cells positively de tected by immunoseparation with subsequent plating was 10(0) cfu/ml. The ap plication of the separation method facilitates a reduction in the time of L isteria detection in cheese by 2 days without affecting the sensitivity. (C ) 2001 Elsevier Science B.V. All rights reserved.