Humanisation of the zebrafish C5a receptor confers targeting by human-specific staphylococcal virulence factors.

Staphylococcus aureus (S. aureus) possesses high host-specificity, including many human-specific virulence factors. Current efforts towards vaccine development have largely failed, citing inappropriate infection models and insufficient understanding of staphylococcal virulence. We sought to create a humanised zebrafish infection model susceptible to human-specific virulence factors, focusing on the human C5a receptor (C5AR1) which is targeted by three human-specific staphylococcal virulence factors, CHIPS, PVL, and HlgCB. We demonstrated that the zebrafish C5a receptor (C5aR) responds to serum-derived zebrafish C5a, mediates phagocyte recruitment, and is not targeted by any adapted staphylococcal virulence factors. In vivo expression of C5AR1 in zebrafish neutrophils conferred susceptibility to PVL and HlgCB and enhanced S. aureus infection. Lastly, we designed a humanised zebrafish C5aR with only three amino acid changes that maintains endogenous signalling capability yet gained sensitivity to CHIPS-mediated inhibition. We show that a partially humanised zebrafish is a valuable model for investigating host-specific virulence factors.