Nanostructured Selenium – A Novel Biologically-Inspired Material for Antibacterial Medical Device Applications - Biomimetics: Advancing Nanobiomaterials and Tissue Engineering - page 206

In this mechanism, selenodiglutathione (GSSeSG) is considered as an
intermediate, which releases element selenium at alkaline pH. Similar to
the alkaline hydrolysis of disulfi de bonds (RSSR) that gives a sulfenic acid
(RSOH) and a thiolate (RS − ) [59], the hydroxide anion is believed to cleave
the selenotrisulphide bond in GSSeSG (step b). This step is favored at alkaline
pH [59], so we need to add NaOH into the solution, and more NaOH results
in the faster reaction. In step c, the release of selenium from the intermedi-
ate selenopersulfi de anion (GSSe − ) is similar to what has been reported for
hydrodisulphide anion (RSS − ) [60]. In fact, the evidence of the occurrence of
selenopersulfi de (GSSe − ) as the initial reaction product has been reported [61].
Because of the small size and higher ratio of surface area to volume com-
pared to conventional selenium materials, selenium nanoparticles were
believed to have different possible mechanisms against bacterial growth
and biofi lm formation, such as the change in hydrophobicity of the surface
preventing bacteria from attachment [62]. It certainly represents a more
natural and biomimetic manner to decrease bacteria attachment.
In a possible mechanism towards inhibiting bacteria, nanostructured
selenium may serve as a catalyst, oxidizing thiol groups, and reducing
oxygen to superoxide [63]. As thiol is an essential substance for bacteria
function, selenium can inhibit bacteria by depleting their thiol levels. This
intracellular thiol depletion mechanism is signifi cant because healthy cells
are more resilient to this effect than bacteria cells. Moreover, the nano fea-
tures of the selenium coating and the change in hydrophobicity that may
have resulted from coating polycarbonate with selenium nanoparticles
[62] may also serve as an important role in inhibiting biofi lm formation.
However, the mechanism of selenium inhibited bacteria growth in bio-
fi lms is likely complicated and further studies are certainly required.

8.4 Selenium Nanoparticles for Antibacterial

Applications

8.4.1 Antibacterial Properties of Selenium Compounds

In several studies, researchers provided the evidence of the antibacterial
properties of many selenium compounds. For example, selenium-enriched
probiotics have been shown to strongly inhibit the growth of pathogenic
Escherichia coli in vivo and in vitro [64]. Escherichia coli was cocultured in vitro
with each of four probiotic strains individually. A cell-free culture super-
natant (CFCS) of each probiotic strain and the four-strain mix were exam-
ined for their antibacterial activity, using the cylinder plate method. In vitro
results demonstrated that cocultures with probiotics signifi cantly reduced
the number of Escherichia coli . The different sizes of inhibition zones made
by each CFCS proved that Escherichia coli was inhibited by the metabolites