Antibacterial Modification of Silicon

Objectives: Aim of this study was to test the ability of three antibacterial agents (AAG) mixed into silicon to induce formation of inhibition zones (IZ) around specimens on agar plates, or the inhibition of bacterial growth in liquid medium.
Methods: Zinc oxide (ZO, 12 concentrations: 0%-30%), copper naphthenate (CN, 11 concentrations: 0%-25%) and silver 2-ethylhexanoate (SEH, 8 concentrations: 0%-10%) were tested in two independent experiments as AAG in silicon.
A) Specimens (n=93, 3/AAG/concentration) were placed on agar plates (lysogeny broth) of Staphylococcus aureus (SA), incubated (37°C, 24h) and inhibition zone (IZ) measured. The test was repeated in case of IZ formation with additional concentrations (n=48, 3/concentration: 2.5%-10%, 0.5% intervals) and statistically analyzed (Spearman correlation, T-test, p<0.05).
B) Half of the specimens (n=124, 4/AAG/concentration) were incubated (37°C, 24h) in pure tryptic soy broth (TSB), the other half in TSB with SA. Bacterial proliferation was measured (optical density, 600nm (OD₆₀₀)) with the pure TSB series as reference, and the results statistically analyzed (T-test, p<0.05).
Results: A) ZO and CN formed no IZ. SEH induced the IZ formation with a strong positive correlation in between concentration and IZ diameter: Spearman correlation (ρ=0.782). Widest IZ, formed at 8% (4.83mm±0.24mm) and 10% (4.92mm±0.12mm), with no significant difference in between both concentrations (T-test, p=0,6856).
B) ZO showed no significant difference in OD₆₀₀ between pure silicon and modified silicon. SEH exhibited a significant increase at 1%-7% (<+0.27A±0.03A) in OD₆₀₀ and an insignificant increase at less than 1% (<+0.04A±0.08A) and 10% (+0.11A±0.18A). CN displayed significant increase in OD₆₀₀ at concentrations of 0.5%-15% (<+0.35A±0.09A), insignificant decrease at 20% (-0.07A±0.14) and significant decrease at 25% (-0.42A±0.05A).
Conclusions: ZO displayed no measurable antibacterial activity. SEH exhibited antibacterial activity in direct contact on agar plates, but none in liquid medium. CN decreased bacterial amount in liquid medium but showed no antibacterial activity on agar plates.