Rapid isolation of K88+ Escherichia coli by using immunomagnetic particles.

Superparamagnetic polymer particles precoated with sheep anti-mouse immunoglobulin G were coated with immunoglobulin G2 monoclonal antibodies to the K88 antigen of Escherichia coli (MAb-K88). These immunomagnetic particles (IMP) were used for isolation and identification of K88 antigen-positive (K88+) E. coli. The bacteria presenting the K88 antigen were easily isolated in almost pure culture from a mixed culture of five different O serogroups of E. coli. Nonspecific binding of K88 antigen-negative (K88-) E. coli to the IMP was not observed. The sensitivity of the test to detect K88+ E. coli was found to be 4,000 CFU/ml with fluorescence microscopy. When bacteria attached to the MAb-K88 IMP were grown on blood agar, about 20% of the initial number of CFU was recovered. The test is promising as a rapid method for isolation and identification of K88+ E. coli from a mixed culture.