Group B streptococci and other gram-positive cocci bind to cytokeratin 8

Group B streptococci (GBS) adhere to surface receptors present on epithelia l cells; these receptors include fibronectin and laminin. To identify other possible receptors, plasma membranes from A539 cells, a respiratory tract epithelial cell line, were prepared. These plasma membranes were tested in a protein blot analysis using radiolabeled GBS as a probe. GBS adhered to t wo species, with molecular masses of 50 kDa (p50) and 57 kDa (p57). We conc luded that p50 and p57 correspond to two forms of cytokeratin 8 (CK8) on th e basis of the following results: (i) protein blot results demonstrated tha t p50 and p57 exactly comigrated with two forms of CK8 after separation by sodium dodecyl sulfate-polyacrylamide gel electrophoresis (PAGE); (ii) p50 and p57 exactly comigrated with CK8 after separation by two-dimensional PAG E; (ii) CK8 in solution bound to GBS, as demonstrated by immunoblot analysi s of proteins from A549 lysates that bound to GBS in a liquid-phase assay; and (iv) radiolabeled GBS bound to A549 lysate-derived CK8 that had been ca ptured in anti-CK8-coated microtiter wells. CK8 bound to COH1-13, an acapsu lar mutant of COH1, demonstrating that adherence is not mediated by capsula r polysaccharide, Trypsin-treated GBS did not bind to CK8, indicating that adherence is mediated via a protein on the surface of GBS. Soluble CK8 boun d to six of six GBS strains tested. Soluble CK8 also bound to Staphylococcu s aureus, Lactococcus lactis, Enterococcus faecalis, and Streptococcus pyog enes. We hypothesize that adherence of GBS to cytokeratin may be important for maintenance of colonization at sites of keratinized epithelium, such as the vagina, or for adherence of these bacteria to damaged epithelial cells at other sites.