Study of Biofilm Inhibition in Oral Pathogens by Nanodiamonds

The complex microbial community, e.g., biofilms residing in our oral cavity, have recognized the clinical significance, as they are typically the main causes of infections. Particularly, they show high resistance to conventional antibiotics, and alternatives including nanotechnology (e.g., bactericidal nanoparticles) are being intensively explored nowadays to provide more efficient therapeutics. The diamond nanoparticles, namely nanodiamonds (NDs), with many promising physico-chemical properties, have attracted significant growth of interest in their biomedical usage over recent years. Despite extensive works using NDs as labeling, imaging, sensing, and drug delivery agents in mammalian cells, only a limited number of studies have been conducted with bacterial (or fungal) cells. For example, the detonation NDs have been demonstrated to work as an effective antibacterial agent against planktonic cells (free-floating state) in the most studied model system <i>Escherichia coli</i>. However, little is known about the behaviors of NDs against biofilms (sessile state). Contrary to the commonly used detonation NDs, the promising (ultrapure, robust, biocompatible, and fluorescent) high-pressure high-temperature (HPHT) counterpart with stable color centers has been chosen in the current study. Here, for the first time, we have performed systematic microbiological studies of high-quality HPHT NDs on several oral and systemically important pathogens. Those “on purpose” chosen microorganisms include fungi (<i>Candida</i><i> albicans </i>and<i> Candida glabrata</i>) and bacteria (<i>Streptococcus</i><i> mutans</i> and <i>Porphyromonas gingivalis</i>), all of which are known to cause common human oral diseases. From the determined sub-inhibitory concentration by the routine test of HPHT NDs on planktonic cells, we have further investigated their capability of inhibition, as well as their role in gene regulation during biofilm formation. Furthermore, we also studied the effects of NDs on disrupting preformed biofilms, in a time and concentration dependent manner. These achievements further our mechanistic understanding of NDs on oral pathogens, paving the way for their clinical and translational applications such as drug carriers and/or additives in the human oral cavity.