Antibody response of dairy cattle experimentally infected with Listeria monocytogenes

The purpose of our study was to monitor the humoral immune response of 34 lactating dairy cattle experimentally infected with Listeria monocytogenes (strain Scott A, serotype 4b). Twenty-seven animals were inoculated with 10(6) to 10(7) c.f.u./ml of L. monocytogenes via the intramammary route at ten day intervals for one month and 7 were inoculated with 4 x 10(2) to 4 x 10(3) c.f.u./ml. Preinfection and weekly-post infection serum and whey samples were prepared during acute infection. Antibody titres of serum and whey were evaluated in agglutination tests using whole-cell formalin-fixed L. monocytogenes suspensions. Preinfection agglutination titres ranged from 1:20 to 1:320. At least four-dilution increase over pre-infection titres were apparent by the 8th week of infection. Eighty per cent of the bovine sera (26/34) exhibited titres of greater than or equal to 1:20, 480. Whey titres, which reflected the local humoral response to L. monocytogenes, rarely exceeded 1:256 which may be ascribed in part to the lower immunoglobulin concentration in milk vs. blood. Antibody levels indicate active listeriosis but could not be used to predict the magnitude of the recovery of Listeria (c.f.u./ml) in milk.