Enhancing curcumin's solubility and antibiofilm activity via silica surface modification

Bacterial biofilms are microbial communities in which bacterial cells in sessile state are mechanically andchemically protected against foreign agents, thus enhancing antibiotic resistance. The delivery of activecompounds to the inside of biofilms is often hindered due to the existence of the biofilm extracellularpolymeric substances (EPS) and to the poor solubility of drugs and antibiotics. A possible strategy toovercome the EPS barrier is the incorporation of antimicrobial agents into a nanocarrier, able topenetrate the matrix and deliver the active substance to the cells. Here, we report the synthesis ofantimicrobial curcumin-conjugated silica nanoparticles (curc-NPs) as a possibility for dealing with theseissues. Curcumin is a known antimicrobial agent and to overcome its low solubility in water it wasgrafted onto the surface of silica nanoparticles, the latter functioning as nanocarrier for curcumin intothe biofilm. Curc-NPs were able to impede the formation of modelP. putidabiofilms up to 50% anddisrupt mature biofilms up to 54% at 2.5 mg mL 1. Cell viability of sessile cells in both cases was alsoconsiderably affected, which is not observed for curcumin delivered as a free compound at the sameconcentration. Furthermore, proteomics of extracted EPS matrix of biofilms grown in the presence offree curcumin and curc-NPs revealed differences in the expression of key proteins related to celldetoxification and energy production. Therefore, curc-NPs are presented here as an alternative forcurcumin delivery that can be exploited not only to other bacterial strains but also to further biologicalapplications.