Silver-substituted hydroxyapatite inhibits Pseudomonas aeruginosa outer membrane protein F: A potential antibacterial mechanism.

Bone fractures are one of the most common injuries, and they have a big effect on population health worldwide. Traumatic bone injuries can be partially treated with implanting bone-graft substitutes, for example, hydroxyapatite (HA), a bioceramic that is similar materially to natural bones with good bioactivity and osteoconductivity. It could, however, be vulnerable to infections because of the way an HA-based bone graft is put in, which could be a weakness in the host's defense. This study incorporated silver (Ag) into hydroxyapatite (Ag-HA) and silicon-containing hydroxyapatite (AgSi-HA) discs to combat this implant-triggered infection. Further, we investigated the antibacterial activities and potential underlying mechanism against a gram-negative bacterium, Pseudomonas aeruginosa. We noticed that the rich calcium (Ca) content in HA discs could trigger the change in P. aeruginosa physiology that leads to the enhanced bacterial growth on non‑silver incorporated HA discs. But the released Ag from Ag-HA and AgSi-HA discs caused significant damage to bacterial cells at a low concentration of 0.3 ppm. We also observed dramatic morphological changes of Ag-HA and AgSi-HA surface-attached bacteria cells. Finally, we identified a potential action mechanism - the surface-bound Ag from Ag-HA and AgSi-HA potently inhibited the outer membrane protein F (OprF) expression of P. aeruginosa. Collectively, our results indicate that incorporating silver ions into HA could contribute viably to excellent antibacterial activities against P. aeruginosa to prevent HA-based bone graft infection.