Escherichia coli

The minimum inhibition concentrations (MICs) of test samples and the positive control drug gentamycin were measured by the microdilution broth susceptibility assay [24 ] against the bacteria Escherichia coli (DSMZ 1058), Bacillus subtilis (DSMZ 704), Pseudomonas agarici (DSMZ 11810), Micrococcus luteus (DSMZ 1605), and Staphylococcus warneri (DSMZ 20036), obtained from DSMZ, Germany. The inocula of bacterial strains were prepared from 12 h broth cultures, and suspensions were adjusted to 0.5 McFarland standard turbidity. The samples were dissolved in 10% DMSO and diluted twofold in sterile 96-well microtiter plates, in duplicate, using BHI broth. Standardized inocula of test strains were added, and after incubation at 37 °C for 24 h on a rotary shaker at 200 rpm, MICs were read as the lowest concentration with inhibition of the growth of the test organisms, compared to the positive control gentamycin and medium containing 10% DMSO as negative control.

Enterococcus moraviensis (DSM 15919), Staphylococcus carnosus (DSM 20501), Acinetobacter kookii (DSM 29071), Pseudomonas stutzeri (DSM 5190), Escherichia coli (DSM 1607), and Enterococcus faecium (DSM 17050) were obtained from DSMZ (Deutsche Sammlung für Mikroorganismen und Zellkulturen, Braunschweig, Germany). Staphylococcus aureus (ATCC 43300), Klebsiella pneumoniae (ATCC 700603), Acinetobacter baumannii (ATCC 19606), and Pseudomonas aeruginosa (ATCC 27853) were obtained from American Type Culture Collection (ATCC, Manassas, VA, United States). Escherichia coli BSU1286 was obtained from the Institute of Medical Microbiology and Hygiene (University Hospital Ulm, Germany). All strains were cultivated to mid-exponential phase and then centrifuged at 7,000 g for 5 min. The resultant pellet was resuspended in phosphate buffered saline (PBS) and washed in PBS, before the suspension was diluted to the desired population density between 5 × 10⁷ and 10⁸ colony forming units per ml (CFU/ml) for experimental use. All experiments were conducted in PBS to avoid the possible photosensitizing impact and absorbance of medium ingredients. Media that were used for cultivation are listed in Table 1.

Staphylococcus aureus (ATCC, 25923, Manassas, VA, USA), Escherichia coli (6899, DSMZ, Germany), Enterobacter cloacae (30054, DSMZ, Germany), and Pseudomonas putida (6125, DSMZ, Germany) were grown to the log phase in 15 mL Lauria broth (LB) (Himedia, M575, Thane West, India) in 50 mL tubes for about 5 h. Each culture was diluted to 0.8 ± 0.05 OD.
The artificial wastewater included 1 mL of each strain in LB (total of 4 mL) along with 10 mL yeast extract (7184A Neogen, Lexington, KY, USA), 69 mL Geobacter medium, and 17 mL phosphate buffer (PB) pH 6.8.

All solvents (tetrahydrofuran (THF) and ethanol (EtOH)) were of UV-spectroscopic grade, purchased from Sigma-Aldrich, and used as received. The 100 nm PS NP were purchased from Kisker Biotech and ultrasonically treated prior to use. The fluorescent dyes NR and FITC were purchased from Fluka and Sigma-Aldrich, respectively, and employed without further purification. Escherichia coli were purchased from DSMZ-German collection of microorganisms and cell cultures. All cell culture materials and ingredients were obtained from Sigma-Aldrich/Merck and Thermo Fisher Scientific.

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.