Synergistic Antibacterial Effect of Silver Nanoparticles Combined with Ineffective Antibiotics on Drug Resistant Salmonella typhimurium DT104

Synergistic antibacterial activity of combined silver nanoparticles (AgNPs) with tetracycline (polykeptide), neomycin (aminoglycoside), and penicillin (-lactam) was tested against the multidrug resistant bacterium Salmonella typhimurium DT104. Dose-dependent inhibition of Salmonella typhimurium DT104 growth is observed for tetracycline-AgNPs and neomycin-AgNPs combination with IC50 of 0.07g/mL and 0.43g/mL, respectively. There is no inhibition by the penicillin-AgNPs combination. These results suggest that the combination of the ineffective tetracycline or neomycin with AgNPs effectively inhibits the growth of this bacterium. The synergistic antibacterial effect is likely due to enhanced bacterial binding by AgNPs assisted by tetracycline or neomycin, but not by penicillin.