Antibacterial and antifouling properties of lipophilic bismuth compounds
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2014 Nova Science Publishers, Inc. All rights reserved. The medicinal and biological properties of elemental bismuth are known to beenhanced by chelating it with lipophilic thiols. In this chapter, we summarize theantibacterial and antifouling potential of selected lipophilic bismuth compoundslargely in the context of environmental, medical, and biotechnologicalapplications. We synthesized ionic and nanoparticulate forms of lipophilicbismuth and determined their minimum inhibitory concentrations (MICs) underenvironmentally relevant conditions for several Gram-negative bacteria. Bacterialproduction of extracellular polymeric substances can be effectively suppressedby bismuth thiols at sub- or near-MIC concentration with negligible effect ongrowth. We focus on a cationic di-thiol, viz. bismuth-2, 3-dimercapto-1-propanol(BAL) prepared using a 2:1 Bi:BAL molar ratio since it is stable over a wide pH range and does not carry the malodor or toxicity of BAL. This BisBALformulation is particularly effective in inhibiting bacterial cohesion and adhesioneven at sub-MICs by decreasing EPS secretion, inhibiting acetylation andcarboxylation of polysaccharides, and altering protein secondary structures. Results indicate that bismuth thiols could be used to probe and mechanisticallyunderstand specific roles of cell-bound and free-EPS in bioflocculation,cohesion, and adhesion without affecting growth. We also synthesizedrhombohedral crystalline BisBAL nanoparticles by reducing the BisBALaqueous complex using an ice-cold solution of sodium borohydride. Thesenanoparticles also inhibited bacterial growth, prevented bacterial attachment tosurfaces, and impaired preformed/established biofilms. We therefore hypothesizethat embedding bismuth nanoparticles will impart antimicrobial and antifoulingproperties to surfaces given their high surface area-to-volume ratio and theirability to slowly release bioactive bismuth in situ over long timeframes due totheir lipophilicity. This may provide the basis for developing bismuthnanoparticlebased broad-spectrum antimicrobial agents, which could "seek anddestroy" microorganisms in a variety of practical applications.
