Monoclonal antibodies against the ruminal bacterium Selenomonas ruminantium

Monoclonal antibodies were raised against whole cells of two different strains of Selenomonas ruminantium and tested for specificity and sensitivity in immunofluorescence and enzyme-linked immunosorbent assay procedures. Species-specific and strain-specific antibodies were identified, and reactive antigens were demonstrated in solubilized cell wall extracts of S. ruminantium. A monoclonal antibody-based solid-phase immunoassay was established to quantify S. ruminantium in cultures or samples from the rumen, and this had a sensitivity of 0.01 to 0.02% from 10(7) cells. For at least one strain, the extent of antibody reaction varied depending upon the stage of bacterial growth. Antigen characterization by immunoblotting shows that monoclonal antibodies raised against two different strains of S. ruminantium reacted with the same antigen on each strain. For one strain, an additional antigen reacted with both monoclonal antibodies. In the appropriate assay, these monoclonal antibodies may have advantages over gene probes, both in speed and sensitivity, for bacterial quantification studies.