Helicid: A novel Anti-Staphylococcus aureus adjuvant

Staphylocoagulase (Coa) plays a critical role in the pathogenicity of Staphylococcus aureus (S. aureus). The present study was undertaken to investigate the underlying mechanism which helicid (HEL) suppressed the virulence factor Coa, as well as to assess the synergistic inhibitory effects of HEL in conjunction with antibiotics, thereby establishing the potential of HEL as an antibacterial adjuvant. We employed coagulation and biofilm assays to comprehensively assess the inhibitory impact of HEL on S. aureus pathogenicity. The thermal shift assay demonstrated that HEL exerted a direct impact on the protein stability of Coa, evidenced by a 6 °C change in melting temperature (ΔTm) at a concentration of 100 μM. HEL binding to Coa proteins was further validated by molecular dynamics simulations and fluorescence quenching. Molecular docking and point mutation assays identified S23 and D112 as crucial binding sites for HEL and Coa. Furthermore, HEL has been observed to potentiate the bactericidal properties of ceftaroline fosamil (CEF-F), concurrently diminishing the resistance exhibited by S. aureus towards CEF-F, as demonstrated by antibiotic synergy tests and resistance induction assays. The combination of HEL and CEF-F effectively reduced the number of bacteria and improved the survival of both Galleria mellonella larvae and mice. Additionally, a significant decrease was observed in the levels of TNF-α, IL-6, and IFN-γ in mice broncho-alveolar lavage fluid (BALF). Ultimately, our findings confirmed that the direct binding of HEL to Coa could diminish the pathogenicity of S. aureus. Moreover, the combination with CEF-F substantially reduced the lethality associated with S. aureus-infected pneumonia and extended the efficacy of the antibiotic.