Staphylococcus aureus targets the purine salvage pathway to kill phagocytes

Staphylococcus aureus colonizes large segments of the human population and causes invasive infections due to its ability to escape phagocytic clearance. During infection, staphylococcal nuclease and adenosine synthase A convert neutrophil extracellular traps to deoxyadenosine (dAdo), which kills phagocytes. The mechanism whereby staphylococcal dAdo intoxicates phagocytes is not known. Here we used CRISPR-Cas9 mutagenesis to show that phagocyte intoxication involves uptake of dAdo via the human equilibrative nucleoside transporter 1, dAdo conversion to dAMP by deoxycytidine kinase and adenosine kinase, and signaling via subsequent dATP formation to activate caspase-3-induced cell death. Disruption of this signaling cascade confers resistance to dAdo-induced intoxication of phagocytes and may provide therapeutic opportunities for the treatment of infections caused by antibiotic-resistant S. aureus strains.

Methicillin-resistant Staphylococcus pseudintermedius synthesizes deoxyadenosine to cause persistent infection

Methicillin-resistant Staphylococcus pseudintermedius (MRSP) is an emerging zoonotic pathogen of canine origin that causes an array of fatal diseases, including bacteremia and endocarditis. Despite large-scale genome sequencing projects have gained substantial insights into the genomic landscape of MRSP, current knowledge on virulence determinants that contribute to S. pseudintermedius pathogenesis during human or canine infection is very limited. Using a panel of genetically engineered MRSP variants and a mouse abscess model, we here identified the major secreted nuclease of S. pseudintermedius designated NucB and adenosine synthase A (AdsA) as two synergistically acting enzymes required for MRSP pathogenesis. Similar to Staphylococcus aureus, S. pseudintermedius requires nuclease secretion along with the activity of AdsA to degrade mammalian DNA for subsequent biosynthesis of cytotoxic deoxyadenosine. In this manner, S. pseudintermedius selectively kills macrophages during abscess formation thereby antagonizing crucial host immune cell responses. Ultimately, bioinformatics analyses revealed that NucB and AdsA are widespread in the global S. pseudintermedius population. Together, these data suggest that S. pseudintermedius deploys the canonical Nuc/AdsA pathway to persist during invasive disease and may aid in the development of new therapeutic strategies to combat infections caused by MRSP.

Immunotherapy Targeting Adenosine Synthase A Decreases Severity of Staphylococcus aureus Infection in Mouse Model

Staphylococcusaureus is a severe pathogen found in the community and in hospitals. Most notably, methicillin-resistant S. aureus (MRSA) is resistant to almost all antibiotics, which is a growing public health concern. The emergence of drug-resistant strains has prompted the search for alternative treatments such as immunotherapeutic approaches. Previous research showed that S. aureus exploit the immunomodulatory attributes of adenosine to escape host immunity. In this study, we investigated adenosine synthase A (AdsA), an S. aureus cell wall-anchored enzyme as possible targets for immunotherapy. Mice vaccinated with aluminum hydroxide-formulated recombinant AdsA (rAdsA) induced high-titer anti-AdsA antibodies, thereby providing consistent protection in 3 mouse infection models when challenged with 2 S. aureus strains. The importance of anti-AdsA antibody in protection was demonstrated by passive transfer experiments. Moreover, AdsA-specific antisera promote killing S. aureus by immune cells. Altogether, our data demonstrate that the AdsA is a promising target for vaccines and therapeutics development to alleviate severe S. aureus diseases.