Quantitative test for Bacteroides nodosus pilus protein by an agglutination-absorption test

A pili agglutination-absorption test (PAAT) was developed for the quantitative measurement of pilus protein in cultures of Bacteroides nodosus and to quantify pili yields during purifications. The test was calibrated by recording the amount of pilus protein required to absorb a measurable amount of anti-pili antibody from antiserum. The amount of anti-pilus antibody in absorbed and unabsorbed serum was specifically measured by a Bact. nodosus K-agglutination test. The PAAT could be calibrated using any combination of crude or pure pili preparations and specific anti-pili serum or non-specific anti-Bact. nodosus serum. This had advantages over the use of radioimmunoassay (RIA) and enzyme-linked immunosorbent assay (ELISA) techniques for measurement of pili because they require the use of highly purified reagents for calibration. The minimum quantity of pilus protein measurable by PAAT was 0.1 microgram per test which was similar in sensitivity to that reported for RIA and ELISA. The reagents used in PAAT were stable for at least six months. The amount of pilus protein per bacterium as measured by PAAT was directly proportional to the average number of pili per bacterium as measured by electron microscopy. The test was Bact. nodosus serotype specific.