ESCHERICHIA-COLI STRAINS WITH NONIMMUNE IMMUNOGLOBULIN-BINDING ACTIVITY

We have identified several strains of Escherichia coli which contain i mmunoglobulin-binding activity on the cell surface. Affinity-purified antibodies ordinarily used as secondary antibodies in immunodetection protocols were bound by 6 of 72 strains of the ECOR reference collecti on off. coli. The Fc fragments of both human and sheep immunoglobulin G (IgG) were also bound, demonstrating the nonimmune nature of the phe nomenon. Binding of conjugated IgG Fe directly to unfixed cells was ob served by fluorescence microscopy. Western blots showed that the immun oglobulin-binding material occurs in the form of multiple bands, with the apparent molecular masses of the most prominent bands exceeding 10 0 kDa. No two of the strains have the same pattern of bands. The bindi ng activity in extracts was sensitive to proteinase K. The binding act ivity of intact cells was reduced preferentially by trypsin digestion, demonstrating exposure at the cell surface. Expression of binding act ivity in Luria-Bertani broth cultures was favored by a temperature of 37 degrees C and entry into stationary phase of growth.