Speed detection of Salmonella.

Poultry-borne salmonellosis is the most common foodborne infection. The cost of the disease to society in terms of absence from work, morbidity and mortality is substantial. Conventional techniques used to detect Salmonella in foods generally require up to 96 hours to show results. If the incidence of the illness is to be reduced, there is a need for rapid, sensitive and simple detection methods for Salmonella in foods that may be contaminated.

Sira Technologies has held the patent on a solid-phase immunobead assay (S-PIA) that has been used successfully in detecting ciguatoxin and okadaic acid. The goal of scientists at Louisiana State University was to select the membrane and immunobead solution (IS) protocol for creating an S-PIA that can detect Salmonella. They also wanted to establish the detection limit of the assay.

Four different membranes were tested with four different IS protocols. An IS was developed with polystyrene microspheres coated with Salmonella monoclonal antibody. There was a variation in the amount of antibody used as well as in the dimensions of the microspheres (0.35 mm and 0.65 mm). Broth inoculated with inactive S. typhimurium and S. enteritidis was used as positive control throughout the experiment.

Researchers placed membranes in contact with the sample. They then immersed them in the IS and evaluated the response. Positive samples were characterized by the development of color on the membranes' surfaces. The criteria applied to the selection of the membrane. An adequate IS was based on the color development and the migration of beads toward the antibody line. Just one membrane and one IS were found to be suitable for the assay.

The detection limit for this array was 6.7x[10.sup.4] cfu per ml. This technique is advantageous because it is rapid and easy to use. Researchers believe that because of its sensitivity, it is a useful tool for the prompt detection of Salmonella in foods. Further information. Carlos E. Ayala, Department of Food Science, Louisiana State University, Louisiana Agricultural Experiment Station, Baton Rouge, LA 70803; phone: [phone]; fax: [phone]; email: [e-mail].