Development and evaluation of a 24-hour method for the detection and quantification of Listeria monocytogenes in meat products

A 24-h filter monitor-based test, Listeria-SELeCT, has been developed to quantify Listeria monocytogenes organisms in meat samples with a sensitivity of less than or equal to 1.0 CFU/g. The technique comprises a filter monitor-based system and a colony lift immunoassay to identify and enumerate the target organism. Meat homogenates were centrifuged and the eluate was filtered to trap and immobilize the microorganisms on the filter. Fraser broth was then added to the filter apparatus to allow the organisms to become established overnight and to inhibit contaminants, after which the filters were transferred onto Modified Oxford medium agar, a selective medium for L. monocytogenes. After 10 to 12 h, a colony lift immunoassay was used to confirm and enumerate suspect colonies on the filter. A correlation study between the Listeria-SELeCT method and the most probable number technique showed the Listeria-SELeCT to be considerably more accurate than the most probable number for quantitatively determining the number of viable organisms in meat samples. Because of ease and speed of testing, the Listeria-SELeCT system also provided major advantages over the most probable number technology.