In vitro antibacterial biofilm effect of magnesium oxide nanoparticles on Streptococcus mutans

Viridans streptococci account for about half of the microbial population inside the mouth, and they are among the major etiological agents of plaque formation and tooth decay. Streptococcus mutans is a member of this group which acts as the major cause of dental decay through the formation of biofilms and acid secretion. In the present study, antibacterial effect of magnesium oxide nanoparticles (NPs) on Streptococcus mutans was evaluated. The NPs used in the present study were chemically synthesized and their properties were confirmed by means of a double-beam ultraviolet-visible spectrometer, an X-ray diffractometer under CuKα beam emission, and a transmission electron microscope. Subsequently, the effect of these NPs on Streptococcus mutans was evaluated using disc diffusion method and optical density measurement in the growth medium. Eventually, the anti-biofilm effect was calculated. Our results on NPs indicated that the largest effect in solid growth medium belongs to a NPs concentration of 15 μgml-1, which established a larger non-growth halo compared to other concentrations. In liquid growth medium, concentration of 5μgml-1 did not have any significant effect, but the two other concentrations remarkably affected bacterial growth rate (p<0.05). These NPs had favorable anti-biofilm properties in a way that they resulted in significant reduction in cell adhesion and biofilm formation at p<0.05 level. It was concluded that magnesium oxide NPs have a significant antibacterial effect on Streptococcus mutans and this effect is dependent on the dose and duration of contact of these NPs with the bacteria.