When cross-reaction is welcome: Monoclonal antibody anti-PBP2a from methicillin-resistant Staphylococcus aureus (MRSA) binds PBP5 from Enterococcus faecium and confers protection in a murine model.

Abstract

Infections caused by methicillin-resistant Staphylococcus aureus (MRSA) and vancomycin-resistant enterococci (VRE) pose significant global concerns, particularly with the limited availability of new antibiotics. Therefore, alternative treatment approaches are needed. In this study, the potential cross-reactivity of a monoclonal antibody (mAb) that binds to MRSA PBP2a, previously described and characterized, was investigated with PBP4 and PBP5 from E. faecalis and E. faecium, respectively, regarding protection against enterococcal infections. In silico analyses evaluated mAb interactions with PBP2a, PBP5, and PBP4 and identified 18 residues involved in anti-PBP2a interactions that shared 33 % and 44 % identity with PBP4 and PBP5, respectively. Significant differences in residue conservation were observed, with 44 % and 22 % conservation observed between PBP2a, PBP5, and PBP4, respectively. The mAb successfully recognized 12 E. faecium strains via western blotting, demonstrating binding to PBP5 polymorphisms, but not to E. faecalis strains. Nano-ITC analysis revealed a strong association between mAb and PBP5 at the nanomolar scale. Immunofluorescence assays confirmed mAb recognition by MRSA and E. faecium, but not by E. faecalis. In vivo, mAb provided protection in a murine model infected with vancomycin-resistant E. faecium, demonstrating the efficacy of the prophylactic treatment. This study underscores the potential of mAb against PBP2a in MRSA for cross-reactivity with PBP5 in E. faecium, offering promising venues for combating infections by antimicrobial-resistant enterococci. AIM: To perform in silico analysis of mAb and PBP2a, PBP5 and PBP4 from MRSA, E.faecium, and E.faecalis, respectively, and to compare cross-reactivities and potential protective effects.