RAPID DETECTION OF SALMONELLAE IN FOODS BY MEMBRANE FILTER‐DISC IMMUNOIMMOBILIZATION TECHNIQUE

Abstract

ABSTRACTA membrane filter‐disc immunoimmobilization technique was developed for rapid detection of salmonellae in foods. The method involved concentrating bacteria from the selective enrichment culture of a food sample by membrane filtration. The membrane filter, with the entrapped bacteria, was inverted and placed on the surface of a semi‐solid selective medium contained in a 100 × 15 mm plastic Petri plate. A paper disc impregnated with Salmonella polyvalent flagellar antiserum was placed on the surface of the semi‐solid agar approximately 2.5 cm from the nearest edge of the membrane filter. The plate was incubated at 37° C under high humidity. Motile salmonellae, if present in the sample, grew and migrated in the semi‐solid medium. When the moving front of motile salmonellae came into contact with the diffusing flagellar antiserum, an antigen‐antibody reaction occurred resulting in the immobilization of salmonellae. The formation of a line of immobilization indicated the presence of salmonellae in the sample. A semi‐solid medium containing dulcitol, proteose peptone, brilliant green, and novobiochin as the major functional components was found to be more efficient than semi‐solid modifications of Salmonella‐Shigella agar and Hektoen enteric agar for the detection of salmonellae in foods by the membrane filter‐disc immunoimmobilization procedure. The new method, when applied to the detection of salmonellae in raw meats and poultry, was found to give good correlation with the conventional cultural method.