Promotion of opsonization by antibodies and phagocytosis of Gram-positive bacteria by a bifunctional polyacrylamide

This paper describes the application of a bifunctional polyacrylamide (pA-V-F) presenting both vancomycin and fluorescein groups, to modify the surfaces of multiple species of Gram-positive bacteria (Staphylococcus aureus, Staphylococcus epidermidis, Streptococcus pneumoniae, and Enterococcus faecalis) to control molecular recognition of these surfaces. The vancomycin groups allowed the specific recognition of a structural component of the bacterial cell wall: peptides terminated in D-Ala-D-Ala. The fluorescein groups allowed the imaging of binding of polymer to the surfaces of bacteria by fluorescence, and are representative, low molecular weight haptens; their recognition by anti-fluorescein antibodies provides proof-of-principle that bifunctional polymers can be used to introduce haptens onto the surface of the bacteria. Flow cytometry revealed that polymer-labeled S. aureus and S. pneumoniae were opsonized by anti-fluorescein antibodies similar to 20-fold more than were untreated bacteria; nearly all (similar to 92%) polymer-labeled S. aureus, and a large (76%) fraction of polymer-labeled S. pneumoniae were opsonized. The bound antibodies then promoted phagocytosis of the bacteria by cultured J774 macrophage-like cells. Flow cytometry revealed that macrophages ingested S. aureus decorated with the polymer-antibody complexes similar to 2-fold more efficiently than S. aureus in control groups, in spite of the high background (caused by efficient antibody-independent ingestion of S. aureus by macrophages). This paper, thus, demonstrates the ability of a bifunctional polymer to carry out three distinct functions based on polyvalent molecular recognition: (i) recognition of the surface of Gram-positive bacteria, (ii) modification of this surface to generate specific binding sites recognized by an antibody, and (iii) promotion of phagocytosis of the opsonized bacteria. (c) 2006 Elsevier Ltd. All rights reserved.