Antimicrobial Coatings to Prevent Biofilm Formation on Medical Devices - Antibiofilm Agents: From Diagnosis to Treatment and Prevention - page 186

Fig. 2 Organoselenium catalyzes the formation of superoxide radicals. Selenium promotes
bacterial toxicity through the catalytic production of the short-lived superoxide radical on the
surface of any material to which it is attached. As seen in the reaction above, the molecule R-Se is
regenerated. Thus, RSe is catalytic and is not changed by the reaction. The other important
component in the reaction is free sulfhydryls. Sulfhydryl species are abundant in all body fluids.
Many bacterial membranes also contain sulfhydryl groups

and medical devices such as intravenous catheter, contact lenses, and block the
formation of Staphylococcus aureus and Pseudomonas aeruginosa biofilms (Low
et al. 2011 ; Mathews et al. 2006 ; Reid et al. 2010 ; Tran et al. 2009 , 2012b ) (Table 1 ).
Concentrations of organo-selenium as low as 0.1 % or 0.2 % were sufficient to
inhibit bacterial attachment to these materials. As can be seen in Fig. 2 , an organo-
selenium molecule can serve as a reducing agent and donate electrons to oxygen.
This oxidized selenium molecule can then become reduced back to its original state
by obtaining electrons from sulfhydral compounds. In vivo a large source of
sulfhydral compounds is glutathione, which is found in body fluids at around
150

M.
It is important to remember that although selenium has the ability to catalyze the
formation of superoxide radicals, selenium is essential for life (Thomson 2004 )
with a recommended dietary allowance of 55 micrograms per day for both men and
women (Institute for Medicine, Food and Nutrition Board 2000 ). This is because
selenium is incorporated into 25 different proteins in the body (Kryukov
et al. 2003 ). Also, superoxide radicals are utilized as second messengers for normal
cell growth mechanisms. Superoxide radicals in body fluids have an estimated half-
life of 400 ns or less and a diffusion pathway of 55-3,000 nm (Saran and Bors
1989 ). This is probably why no toxicity was observed in corneas from eyes
containing contact lenses coated with organoselenium (Mathews et al. 2006 ). In
addition, cancer patients given milligram quantities of organo-selenium for a year
showed no observed toxicity (Reid et al. 2004 ).

μ