Immunocytochemical labelling of Bacteroides nodosus pili using an immunogold technique

An immunogold labelling technique was used to label the pili of the bacterium Bacteroides nodosus. The labelling was distinct and highly specific, and individual pili could be recognised beneath the gold probe. The labelling of somatic antigens could be distinguished from that of pilus antigens. Furthermore, labelling of fragments of cytoplasm released by cell lysis and trapped in the pili could be distinguished from pilus labelling. An antiserum that had been raised against strain 80200 (serotype N) labelled pili of strain 215 (serotype B). Double labelling experiments with this antiserum and the antiserum against strain 215 (serotype B) showed that both antisera label the same pili bundles. The ease of detection of the immunocytochemical reaction should enable this technique to be used as a routine screen for pilus antigens. It also possesses the potential for much wider applications for immunolabelling other antigens, such as viruses, that can be obtained in suspension.