Identification of cross-reactive vaccine antigen candidates in Gram-positive ESKAPE pathogens through subtractive proteome analysis using opsonic sera

The Gram-positive pathogens of the ESKAPE group, Enterococcus faecium, and Staphylococcus aureus, are well-known to pose a serious risk to human health because of their high virulence and numerous drug resistances, making them a real concern in healthcare settings worldwide. To narrow down the list of previously identified promising protein vaccine candidates, a combination of several antigen discovery approaches was performed, in particular a "false positive analysis" of peptides generated by trypsin shaving with a subtractive proteome analysis. The final list of nine potential antigens included AdcAau, a protein performing the same function as AdcAfm, an already discovered antigen in enterococci. Bioinformatic analyses revealed that AdcAau and AdcAfm share a sequence identity of 41.2% and that the conserved regions had a high antigenicity. AdcAau was selected for further investigation and the results reported in this manuscript demonstrate the opsonic properties of AdcAau-specific antibodies against the S. aureus strain MW2, as well as their cross-binding and cross-opsonic activity against several S. aureus, E. faecium, and E. faecalis strains. This study suggests that further investigation of cross-reactive activities is a valuable tool for discovering new antigens that cover more than one clinically relevant pathogen.