Staphylococcus aureus

Antibacterial properties of the films were investigated by utilizing the agar diffusion method against Gram-negative bacteria Escherichia coli (ATCC 25922), Salmonella enterica subsp. enterica (DSMZ 17420), Gram-positive bacteria Staphylococcus aureus (DSMZ 12463), and Listeria monocytogenes (DSMZ 27575). The tested foodborne microorganisms were obtained from the Institute of Technology of Agricultural Products, ELGO-DEMETER, Lykovryssi, Greece.
Fresh cultures of the bacterial strains were prepared in Mueller Hinton Broth. The cultures were inoculated at 37 °C for 24 h in order to achieve a range of 10⁷–10⁸ CFU mL⁻¹. After that, the bacteria were swabbed on Mueller-Hinton agar dishes by rotating the plate every 60° to ensure consistent growth.
The tested films were cut into 6 mm diameter discs by a circular knife and were placed on a Mueller-Hinton inoculated plate. The dishes were incubated at 37 °C overnight. The diameter of the inhibitory zones, and the contact area of the discs with agar surface, were measured. The experiment was performed thrice.

Lysogeny broth (LB), CASO broth,
safranin, sodium dodecyl sulfate
(SDS), phosphate buffer saline (PBS), and anhydrous tetrahydrofuran
(THF) were obtained from Merck (Diegem, Belgium). Ethanol 70% was
purchased from VWR international, and BacLight bacteria fluorescent
stain from Fisher Emergo (Landsmeer, Netherlands). All reagents were
used as received and had a minimum purity of 99.9%. E. coli (ATCC 8739), E. coli (ATCC 23716), Cronobacter
sakazakii (ATCC 29544), and Staphylococcus aureus (ATCC 6538) strains from DSM-Z (Braunschweig, Germany). Polydimethylsiloxane
Sylgard 184 elastomer kit was purchased from Mavom N.V. (Schelle,
Belgium). Graphene oxide (GO) flakes synthesized following an improved
Hummer’s method^{29 (link)} was provided from
Aachen-Maastricht Institute for Biobased Materials (AMIBM), The Netherlands.
All aqueous solutions were prepared with deionized water with a resistivity
of 18.1 MΩ cm^–1.

Gentamicin sulfate (solubilized in water, 3%, GS, Sigma-Aldrich, St. Louis, MO, USA) was used as an antibiotic. Tetraethylorthosilicate (TEOS, 98%, Aldrich, St. Louis, MO, USA) was used as the silica particle precursor). Octyltriethoxysilane (OTES, 97%, Fluka, Philadelphia, PA, USA) was used as the modifying agent. Isopropyl alcohol (iPrOH, 99.9%, Chimreactiv S.R.L., Bucharest, Romania) was used as the solvent. Aqueous solution of ammonia (NH₄OH, 25%, Sigma-Aldrich, Merck KGaA, Darmstadt, Germany) was used as the catalyst. The chemicals were used as received. The glass substrate was purchased from FabTech (Bucharest, Romania) and was chosen in order to investigate the topography of films obtained by deposition of final materials.
Three fungal strains, Staphylococcus aureus, Pseudomonas aeruginosa, and Escherichia coli), purchased from German Collection of Microorganisms and Cell Cultures (DSMZ) (Braunschweig, Germany), were used in the experiments.