The use of monoclonal antibodies against Listeria monocytogenes in a direct immunofluorescence technique for the rapid presumptive identification and direct demonstration of Listeria in food.

Two monoclonal antibodies which recognise serogroup specific cell surface antigens of Listeria monocytogenes are described. The antibodies were specific for Listeria (i.e. did not react with 87 strains of bacteria from 14 other genera). In an indirect immunofluorescent test the antibodies had similar specificities when tested against strains of L. monocytogenes from human infections grown under a number of different growth conditions, and serological reference strains. A direct immunofluorescent antibody test was developed, and similar specificities of the antibodies found with strains of Listeria which had been isolated from food and grown under 2 different growth conditions. This technique is also used to directly demonstrate Listeria in soft cheese.