ABSTRACT
Staphylococcus aureus is considered to be an extracellular pathogen. However, survival of S. aureus within host cells may provide a reservoir relatively protected from antibiotics, thus enabling long-term colonization of the host and explaining clinical failures and relapses after antibiotic therapy. Here we confirm that intracellular reservoirs of S. aureus in mice comprise a virulent subset of bacteria that can establish infection even in the presence of vancomycin, and we introduce a novel therapeutic that effectively kills intracellular S. aureus. This antibody-antibiotic conjugate consists of an anti-S. aureus antibody conjugated to a highly efficacious antibiotic that is activated only after it is released in the proteolytic environment of the phagolysosome. The antibody-antibiotic conjugate is superior to vancomycin for treatment of bacteraemia and provides direct evidence that intracellular S. aureus represents an important component of invasive infections.
Subject(s)
Anti-Bacterial Agents/pharmacology , Bacteremia , Immunoconjugates/pharmacology , Immunoconjugates/therapeutic use , Intracellular Space/microbiology , Staphylococcal Infections/microbiology , Staphylococcus aureus/drug effects , Vancomycin/pharmacology , Animals , Anti-Bacterial Agents/therapeutic use , Bacteremia/drug therapy , Bacteremia/microbiology , Carrier State/drug therapy , Carrier State/microbiology , Drug Design , Female , Immunoconjugates/chemistry , Intracellular Space/drug effects , Methicillin-Resistant Staphylococcus aureus/drug effects , Methicillin-Resistant Staphylococcus aureus/pathogenicity , Mice , Microbial Sensitivity Tests , Phagosomes/drug effects , Phagosomes/metabolism , Phagosomes/microbiology , Staphylococcal Infections/drug therapy , Staphylococcal Infections/pathology , Staphylococcus aureus/pathogenicity , Vancomycin/therapeutic useABSTRACT
Infection of host tissues by Staphylococcus aureus and S. epidermidis requires an unusual family of staphylococcal adhesive proteins that contain long stretches of serine-aspartate dipeptide-repeats (SDR). The prototype member of this family is clumping factor A (ClfA), a key virulence factor that mediates adhesion to host tissues by binding to extracellular matrix proteins such as fibrinogen. However, the biological siginificance of the SDR-domain and its implication for pathogenesis remain poorly understood. Here, we identified two novel bacterial glycosyltransferases, SdgA and SdgB, which modify all SDR-proteins in these two bacterial species. Genetic and biochemical data demonstrated that these two glycosyltransferases directly bind and covalently link N-acetylglucosamine (GlcNAc) moieties to the SDR-domain in a step-wise manner, with SdgB appending the sugar residues proximal to the target Ser-Asp repeats, followed by additional modification by SdgA. GlcNAc-modification of SDR-proteins by SdgB creates an immunodominant epitope for highly opsonic human antibodies, which represent up to 1% of total human IgG. Deletion of these glycosyltransferases renders SDR-proteins vulnerable to proteolysis by human neutrophil-derived cathepsin G. Thus, SdgA and SdgB glycosylate staphylococcal SDR-proteins, which protects them against host proteolytic activity, and yet generates major eptopes for the human anti-staphylococcal antibody response, which may represent an ongoing competition between host and pathogen.