Titanate-Metal Complex as a Novel Antimicrobial in Dentistry

Objectives: Metal-titanates have a broad spectrum of antimicrobial activities and possess promising antimicrobial properties because of their ability to bypass systemic toxicity. Previous studies showed that metal-titanates could be particularly beneficial in dental materials and treatments. Here, we investigate the mechanism of the antibiotic effect of Au(III)- titanate complex on cariogenic bacteria, Streptococcus mutans and Lactobacillus casei.
Methods: Bacteria were exposed sequentially to 10, 25, 50, 100, 200, and 400 mg/L of Au(III)-titanate to determine their ability to develop resistance. Bacterial counts were determined using optical density reading. Quantitative RT-PCR was used to determine the changes in the expression of the bacterial genes involved in adhesion (srtA and fbpA for L. casei; GTF and Pac for S. mutans). Correlations of gene expression levels between treatment and control groups (no exposure to Au(III)-titanate) were determined by the Pffafl method.
Results: In the resistance study, growth of L. casei continuously decreased compared to the control as the Au(III)-titanate concentration increased. Growth of S. mutans under the same condition significantly dropped at 400 mg/L compared to the control. Expression of srtA in L. casei was increased by 57%, while increase in fbpA was not significant after 18h. Expression of S. mutans glucosyltransferase increased at 4h but significantly decreased by 50% at 18h, while Pac increased by 47% at 18h.
Conclusions: Our data suggests that bacteria may regulate its virulence by compensating for the initial interference on adherence. Our data also suggests that the mechanism behind the antimicrobial activities of Au(III)-titanate against S. mutans is through an interplay of downregulation and upregulation processes involving glucan formation (glucosyltransferase) and initial attachment (Pac). Further studies on the mechanism of microbial growth arrest by Au(III)-titanate will help to determine how this compound can be best utilized to inhibit bacterial infection in dentistry.