Antibacterial Efficacy of AgNPs and AgNPs-PVP
Two gram-positive bacteria, Streptococcus pneumoniae (S. pneumoniae ) and Streptococcus mutans (S. mutans ), and one gram-negative bacteria, non-typeable Haemophilus influenzae(NTHi), were chosen to test antibacterial effects of AgNPs-PVP. In short, S. mutans was cultured in Brian Heart Infusion (BHI) broth (BD Bioscience, USA), and both S. pneumoniae and NTHi were cultured in BHI medium with defibrinated horse blood and nicotinamide adenine dinucleotide (NADH) in a humidified 5% CO2-conatining balanced-air incubator at 37°C according to established protocols48–50.
The suspension assay for estimation of the minimum inhibitory concentration (MIC) values was carries out to evaluate the antibacterial activity. The MIC values were determined on 96-well plates. Bacteria were cultured to serial dilutions of the AgNPs-PVP or AgNPs (3.125 µM, 6.25 µM, 12.5 µM, 25 µM, 50 µM, and 100 µM), and the end time points were determined when control group (bacteria only) grew to the stationary phase. Background from the nanoparticles alone was subtracted from the final reading. All assays were carried out in triplicates. All bacterial growth status were monitored by optical density at a wavelength of 600 nm (OD600) using a UV–Vis Spectrophotometer (Infinite® M1000 PRO).