Effects of the sol-gel route on the structural characteristics and antibacterial activity of silica-encapsulated gentamicin

Abstract

The effects of sol-gel processes, i.e., acid-catalyzed gelation, base-catalyzed 37 gelation and base-catalyzed precipitation routes, on the encapsulation of 38 gentamicin were investigated. The resulting xerogels were characterized using 39 a series of complementary instrumental techniques, i.e., the 40 adsorption/desorption of nitrogen, small-angle X-ray scattering, Fourier 41 transform infrared spectroscopy, diffuse reflectance spectroscopy, X-ray 42 photoelectron spectroscopy, atomic force microscopy and scanning electron 43 microscopy. The encapsulated gentamicin samples were tested against five 44 bacterial strains, including two Gram-positive (Staphylococcus aureus ATCC 45 25923, Bacillus cereus ATCC 11778) and three Gram-negative strains 46 (Escherichia coli ATCC 25922, Enterobacter aerogenes ATCC 13048 and 47 Salmonella typhimurium ATCC 14028). The best antimicrobial activity was 48 observed for the encapsulated gentamicin that was prepared via the 49 precipitation route, even in comparison with the neat antibiotic, especially in the 50 case of the Gram-positive strain Staphylococcus aureus. The gentamicin 51 concentration on the outermost surface and the zeta potential were identified as 52 factors that affected the highest efficiency, as observed in the case of 53 encapsulation via the base-catalyzed precipitation process.