An enzyme immunoassay for measuring Escherichia coli pilus antigens

Quantitative enzyme-linked antibody centrifuge (ELAC) assays have been developed for measuring Escherichia coli adhesion pilus antigens K99, K88, 987P and F41 in E. coli bacterins used for protecting newborn animals against neonatal enteric colibacillosis. The test consists of reacting an alkaline phosphatase conjugate of specific pilus antigen antibody directly with dilutions of the bacterin on test and a standard reference bacterin. Following incubation the unbound conjugate is removed by two centrifugation steps and the bacteria with bound conjugate are reacted with substrate. The optical density is measured at 405 nm. Unknown samples are compared to a standard bacterin known to develop sufficient immunity in sows to provide protective levels of passive maternal immunity to their piglets. A relative potency (RP) value is calculated and used for standardizing bacterial concentrates and for final potency testing. The advantages to be realized are: shortening of the test period, specificity, and reduction in test animal usage.