The objective of this study was to demonstrate that a field isolate of Actinobacillus seminis (As8C) will adhere to epithelial cells and that this adhesion can be inhibited by pretreating the bacteria with mouse serum containing polyclonal antibodies (PoAbs) prepared against this isolate. An indirect fluorescent antibody test, transmission electron microscopy, and phase-contrast microscopy confirmed the adhesion of As8C to an established culture of bovine kidney epithelial cells (BKECs). In a bacterial adhesion assay, 40 As8C were estimated to adhere to each BKEC after 60 min. Using a bacterial inhibition assay, PoAbs diluted 10(-2) or 10(-3) inhibited the adhesion of As8C to BKECs by approximately 90%. Bacterial inhibition decreased to about 50% when the PoAbs were diluted to 10(-4). There was less than 10% inhibition of adhesion of As8C to BKECs when higher dilutions of PoAbs were used. The inhibition of As8C adhesion to BKECs was less than 20% following pretreatment of BKECs with 10(-2) to 10(-5) dilutions of PoAbs. Moreover, pretreatment of As8C with a 10(-2) dilution of PoAbs did not appear to adversely affect bacterial growth on agar. It is likely that the PoAbs interrupted the adhesion of As8C to BKECs by sterically interfering with a bacterial adhesin-epithelial cell receptor interaction.