Peroxotitanate‐ and monosodium metal‐titanate compounds as inhibitors of bacterial growth

Abstract

Sodium titanates are ion-exchange materials that effectively bind a variety of metal ions over a wide pH range. Sodium titanates alone have no known adverse biological effects but metal-exchanged titanates (or metal titanates) can deliver metal ions to mammalian cells to alter cell processes in vitro. In this work, we test a hypothesis that metal-titanate compounds inhibit bacterial growth; demonstration of this principle is one prerequisite to developing metal-based, titanate-delivered antibacterial agents. Focusing initially on oral diseases, we exposed five species of oral bacteria to titanates for 24 h, with or without loading of Au(III), Pd(II), Pt(II), and Pt(IV), and measuring bacterial growth in planktonic assays through increases in optical density. In each experiment, bacterial growth was compared with control cultures of titanates or bacteria alone. We observed no suppression of bacterial growth by the sodium titanates alone, but significant (p < 0.05, two-sided t-tests) suppression was observed with metal-titanate compounds, particularly Au(III)-titanates, but with other metal titanates as well. Growth inhibition ranged from 15 to 100% depending on the metal ion and bacterial species involved. Furthermore, in specific cases, the titanates inhibited bacterial growth 5- to 375-fold versus metal ions alone, suggesting that titanates enhanced metal-bacteria interactions. This work supports further development of metal titanates as a novel class of antibacterials.

Titanates and Titanate-Metal Compounds in Biological Contexts

“…For example, growth of A. naeslundii , a bacterial species implicated in tooth root surface caries (tooth decay) and early childhood caries, was inhibited by Au(III) at concentrations as low as 10μM, but uninhibited by Pt(IV) at concentrations ≤ 750 mM [17]. Similarly, exposure of S. mutans , a bacteria known to cause dental caries, to Au(III) at the concentrations of 1-20 μM decreased bacterial growth, with little difference shown between different concentrations tested.…”

“…Titanate-metal compounds have been reported to inhibit bacterial growth, depending on the type of metal ion and the bacterial species (Figure 6) [17]. An inhibitory effect was observed with MST compounds of Au(III), Pt(IV) or Pd(II) ions [17]; the degree of inhibition varied among metals and bacterial species, but MST-Au(III) showed the greatest effect.…”

“…An inhibitory effect was observed with MST compounds of Au(III), Pt(IV) or Pd(II) ions [17]; the degree of inhibition varied among metals and bacterial species, but MST-Au(III) showed the greatest effect. Growth of A. actinomycetemcomitans, F. nucleatum and P. gingivalis was suppressed by ≥ 50% between concentrations of 1-10 μg/mL, whereas the growth suppression for A. naeslundii started at 50 μg/mL.…”

“…Compared to MST-Au(III), APT-Au(III) was less effective in inhibiting bacterial growth. For example, maximum bacterial growth suppression on A. actinomycetemcomitans and F. nucleatum was reduced from 100% down to 10% and 40%, respectively, for APT-Au(III) compared to MST-Au(III) [17]. Similarly, growth of A. naeslundii was suppressed up to 80% in the presence of MST-Au(III), while APT-Au(III) did not suppress growth of A. naeslundii [17].…”

Synthesis and Reaction Chemistry of Nanosize Monosodium Titanate

“…In vitro tests with the noble metal-exchanged titanates indicate suppression of the growth of cancer and bacterial cells by an unknown mechanism. 8,9 Historically, sodium titanates have been produced using both sol-gel and hydrothermal synthetic techniques resulting in fine powders with particle sizes ranging from a few to several hundred microns. 4,5,10,11 More recently, synthetic methods have been reported that produced nanosize titanium dioxide, metal-doped titanium oxides, and a variety of other metal titanates.…”