Antibiotic resistance has necessitated search for new antibacterials for combating threat of pathogenic bacteria. Though chemically synthesized silver nanoparticles are a well-known antimicrobial agent, they are toxic to human cells at higher concentrations. Hence in the present study, curcumin-silver nanoparticles (Cur-AgNPs) of size 25-35 nm, were synthesized using curcumin, a phytochemical. These nanoparticles were effective against both Gram positive and Gram-negative bacteria and were less toxic to human keratinocytes. They had very low total silver content and high stability. The antibacterial activity of Cur-AgNPs, as studied by minimum inhibitory concentration (MIC = 5 mg/L), time kill kinetics and post agent effect, was better than silver nanoparticles (AgNPs, size ≈ 35 nm, MIC = 20 mg/L). The inhibitory effect of Cur-AgNPs on biofilm formation was also ≈ 20% more than AgNPs as demonstrated by live-dead imaging and scanning electron microscopy. The cytotoxic test to skin keratinocytes (HaCaT) showed that Cur-AgNPs were toxic at a concentration of 156 mg/L which is much higher than the bacterial MIC (selective toxicity). They also showed anti-inflammatory effect on human macrophages (THP1) by reducing secretion of pro-inflammatory cytokines IL-6 and TNF-α as compared to chemically synthesized AgNPs.
Keywords: Antibacterial; Antibiofilm; Curcumin; Macrophage; Minimum inhibitory concentration; Selective toxicity; Silver nanoparticle.