Impact of Graphene Exposure on Microbial Activity and Community Ecosystem in Saliva

Graphene-based nanomaterials (GMs) are served as great promising agents for the prevention and therapy of infectious diseases. However, their dental applications remain to be evaluated, especially under the context of the oral microbial community. Here, we examined the exposure-response of salivary bacterial community to two types of GMs, that is, graphene oxide (GO) and GO-silver nanoparticles (AgNPs). Both GO and GO-AgNPs showed lethal effect against salivary bacteria in a concentration-dependent manner, and the antibacterial capacity of GO-AgNPs is superior to GO. Interestingly, the salivary bacterial community enhanced the tolerance to GMs as compared to homogeneous bacteria. High-throughput sequencing revealed that both 80 μg/mL GO and 20 μg/mL GO-AgNPs significantly altered the biodiversity of salivary bacterial community. Especially, they increased the relative abundance of Gram-positive bacteria compared to the untreated sample, notably Streptococcus, suggesting that the bacterial wall structure plays a critical role in resisting the damage of GMs. Although GMs could effectively limit the salivary bacterial activity and cause changes in bacterial community structure, they are not toxic to mammalian cell lines. We envision this study could provide novel insights into the application of GMs as "green antibiotics" in nanomedicine.