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BackgroundAntibiotic resistance is a global issue that threatens public health. The excessive use of antibiotics contributes to this problem as the genes of antibiotic resistance can be transferred between the bacteria in humans, animals and aquatic organisms. Metallic nanoparticles could serve as future substitutes for some conventional antibiotics because of their antimicrobial activity. The aim of this study was to evaluate the antimicrobial effects of silver and zinc oxide nanoparticles against major fish pathogens and assess their safety in vitro. Silver nanoparticles were synthesized by chemical reduction and characterized with UV–Vis spectroscopy, transmission electron microscopy and zeta sizer. The concentrations of silver and zinc oxide nanoparticles were measured using inductively coupled plasma-mass spectrometry. Subsequently, silver and zinc oxide nanoparticles were tested for their antimicrobial activity against Aeromonas hydrophila, Aeromonas salmonicida subsp. salmonicida, Edwardsiella ictaluri, Edwardsiella tarda, Francisella noatunensis subsp. orientalis, Yersinia ruckeri and Aphanomyces invadans and the minimum inhibitory concentrations were determined. MTT assay was performed on eel kidney cell line (EK-1) to determine the cell viability after incubation with nanoparticles. The interaction between silver nanoparticles and A. salmonicida was investigated by transmission electron microscopy.ResultsThe tested nanoparticles exhibited marked antimicrobial activity. Silver nanoparticles inhibited the growth of both A. salmonicida and A. invadans at a concentration of 17 µg/mL. Zinc oxide nanoparticles inhibited the growth of A. salmonicida, Y. ruckeri and A. invadans at concentrations of 15.75, 31.5 and 3.15 µg/mL respectively. Silver nanoparticles showed higher cell viability when compared to zinc oxide nanoparticles in the MTT assay. Transmission electron microscopy showed the attachment of silver nanoparticles to the bacterial membrane and disruption of its integrity.ConclusionsThis is the first study on inhibitory effects of silver and zinc oxide nanoparticles towards A. salmonicida and A. invadans. Moreover, zinc oxide nanoparticles inhibited the growth of Y. ruckeri. In low concentrations, silver nanoparticles were less cytotoxic than zinc oxide nanoparticles and represent an alternative antimicrobial compound against A. hydrophila, A. salmonicida and A. invadans.

The main objective of this study is to investigate the antibacterial activity of silver nanoparticles (AgNPs) against multidrug-resistant Salmonella isolates recovered from diarrheic sheep and goats Methods: This study used chemical reduction synthesis of AgNPs to evaluate their antimicrobial effects by estimation of minimum inhibitory concentration (MIC) and minimum bactericidal concentration (MBC) for each isolate using the microplate dilution method and tetrazolium salt reduction test to detect the viability percentage. In vivo treatment efficacy was assessed in mice by determining the viable count of Salmonella Enteritidis recovered from feces and by hematologic, biochemical and histopathologic examinations to confirm that use of AgNPs has no toxic or pathologic effects and to evaluate its ability in tissue regeneration following treatment. Results: All recovered strains were identified as MDR with a prevalence of 4% and 3.6% in sheep and goats, respectively. The results of TEM, DLS, Zeta potential, and FTIR revealed typical characteristics of the synthesized AgNPs. Silver nanoparticles showed antibacterial activity against all recovered strains with MIC of ≤0.02-0.313 μg/mL (mean average 0.085 ±0.126 μg/mL) and MBC of 0.078-1.250 μg/mL (average 0.508±0.315 μg/mL). In vivo efficacy of AgNPs was observed by a reduction in the number of viable S. Enteritidis recovered from feces in an S. Enteritidis infected mouse model, with complete shedding stopping between treatment days 4 and 6. Hematologic, serum biochemical, and histopathologic analyses proved the ability of AgNPs to suppress inflammatory reaction caused by S. Enteritidis infection. Conclusion: The study proved the effective ability of AgNPs to fight MDR Salmonella spp. in vitro and in vivo without adverse effects.

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This study aimed to assess the antibacterial efficacy of Gum Arabic‐based silver nanoparticles against certain fish bacterial pathogens. Silver nanoparticles were green‐synthesized using Gum Arabic (AgNPs‐GA), which served as a stabilizing and reducing agent. The AgNPs‐GA were analysed using a UV spectrophotometer set at a wavelength of 450 nm. Transmission electron micrograph analysis showed that nearly all AgNPs‐GA were sphere‐shaped and 10.0 nm in diameter. Dynamic light scattering (DLS) analysis showed a narrow size distribution curve, whose highest peak was at 26.2 nm. The particles were negatively charged (−17.1 ± 4.9 mV). Silver concentration measured by inductively coupled plasma optical emission spectrometry (ICP‐OES) and found to be 104 µg/ml. The in vitro antibacterial activity of AgNPs‐GA was tested against Aeromonas hydrophila and Pseudomonas aeruginosa. Gum Arabic‐silver nanoparticles exhibited clear inhibition zones of 22 and 20 mm against A. hydrophila and P. aeruginosa, with a minimum inhibitory concentration of 1.625 µg/ml and 3.25 µg/ml for AgNPs‐GA respectively. The antibiofilm activity indicated that AgNPs‐GA significantly inhibit A. hydrophila and P. aeruginosa biofilm formation at AgNPs‐GA concentrations of 1.625 µg/ml. There was no significant difference at a AgNPs‐GA concentration of 0.8215 µg/ml between the control‐positive groups and the AgNPs‐GA treatment groups in both bacterial strains. In summary, green‐synthesized sliver nanoparticles display efficient antibacterial properties, which suggests that they would be suitable for use in a commercialized antibacterial product for the aquaculture industry.

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