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Antimicrobial agents have been developed for drug-resistance infections, which have been rapidly increasing; however, the control of involved microorganisms is still a challenge. In this work, SNP with bovine serum albumin (BSA) and chitosan (CS) coatings were prepared with an aqueous reduction method, characterized using dispersion light scattering, transmission electron microscopy, and thermal analysis. Antibacterial activity was tested on seven oral and nonoral bacteria by microdilution test and scanning electron microscopy. Six different sizes and shapes of coated SNP were prepared and used. Characterization revealed narrow size and good distribution of particles, spherical and pseudospherical shapes, and the presence of coatings on the SNP surfaces. All samples showed antimicrobial activity, although smaller sizes and CS samples had the best inhibition effects. The highest microbial resistance was shown by Gram-positive bacteria. Although coated SNP action depends on particular bacterium, BSA and CS coated SNP could be used for drug-resistance infections.

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We have applied epifluorescence principles, atomic force microscopy, and Raman studies to the analysis of the colonization process of pyrite (FeS(2)) by sulfuroxidizing bacteria Acidithiobacillus thiooxidans after 1, 15, 24, and 72 h. For the stages examined, we present results comprising the evolution of biofilms, speciation of S (n) (2-) /S(0) species, adhesion forces of attached cells, production and secretion of extracellular polymeric substances (EPS), and its biochemical composition. After 1 h, highly dispersed attached cells in the surface of the mineral were observed. The results suggest initial non-covalent, weak interactions (e.g., van der Waal's, hydrophobic interactions), mediating an irreversible binding mechanism to electrooxidized massive pyrite electrode (eMPE), wherein the initial production of EPS by individual cells is determinant. The mineral surface reached its maximum cell cover between 15 to 24 h. Longer biooxidation times resulted in the progressive biofilm reduction on the mineral surface. Quantification of attached cell adhesion forces indicated a strong initial mechanism (8.4 nN), whereas subsequent stages of mineral colonization indicated stability of biofilms and of the adhesion force to an average of 4.2 nN. A variable EPS (polysaccharides, lipids, and proteins) secretion at all stages was found; thus, different architectural conformation of the biofilms was observed during 120 h. The main EPS produced were lipopolysaccharides which may increase the hydrophobicity of A. thiooxidans biofilms. The highest amount of lipopolysaccharides occurred between 15-72 h. In contrast with abiotic surfaces, the progressive depletion of S (n) (2-) /S(0) was observed on biotic eMPE surfaces, indicating consumption of surface sulfur species. All observations indicated a dynamic biooxidation mechanism of pyrite by A. thiooxidans, where the biofilms stability and composition seems to occur independently from surface sulfur species depletion.