Ciprofloxacin-Loaded Silver Nanoparticles as Potent Nano-Antibiotics against Resistant Pathogenic Bacteria

Abstract

Silver nanoparticles (AgNPs) have demonstrated numerous physicochemical, biological, and functional properties suitable for biomedical applications, including antibacterial and drug carrier properties. In the present study, the antibiotic, ciprofloxacin (CIP), was loaded onto AgNPs, which were synthesized via the chemical reduction method, thereby enhancing CIP's antibacterial activity against Gram-negative (Acinetobacter baumannii and Serratia marcescens) and Gram-positive (Staphylococcus aureus) bacterial strains. Polyethylene glycol-400 (PEG) was used to prepare an AgNPs-PEG conjugate with enhanced stability and to act as the linker between CIP and AgNPs, to produce the novel nanocomposite, AgNPs-PEG-CIP. The prepared AgNPs and their conjugates were characterized by ultraviolet-visible spectrophotometry, Fourier-transform infrared spectroscopy, X-ray diffraction, field emission scanning electron microscopy with energy-dispersive X-ray spectroscopy, transmission electron microscopy, zeta potential analysis, and dynamic light scattering techniques. The inhibitory activity of AgNPs and their conjugates on the growths of pathogenic bacteria was assessed using the well-diffusion method. The results showed the enhanced antibacterial effects of AgNPs-CIP compared to CIP alone. The AgNPs-PEG-CIP nanocomposite showed excellent inhibitory effects against bacterial isolates, with its inhibition zones diameters reaching 39, 36, and 40 mm in S. aureus, A. baumannii, and S. marcescens, respectively. The minimum inhibitory concentration and minimum bactericidal concentration of fogNPs and their conjugates and their antibiofilm effects were also determined. The antioxidant potentials of AgNPs and their conjugates, tested via their 1,1-diphenyl-2-picryl-hydrazyl (DPPH) scavenging ability, showed that the activity increased with increasing AgNPs concentration and the addition of the PEG and/or CIP. Overall, according to the results obtained in the present study, the new nanocomposite, AgNPs-PEG-CIP, showed the highest antibacterial, antibiofilm, and antioxidant activity against the pathogenic bacteria tested, compared to CIP alone. The preparation has high clinical potential for prospective use as an antibacterial agent.

Keywords: PEG; antioxidant; ciprofloxacin; nanocomposite; pathogenic bacteria; silver nanoparticles.

Figure 1

Schematic representation of the AgNP-PEG-CIP preparation and the molecular interaction sites (OH, NH, (C=O)-OH, and C=O) between the PEGs and the CIP molecules.

Figure 2

Chemical structure models of the AgNP-PEG-CIP (two methylene units,-CH₂-CH₂, of the AgNP-PEG, i.e., AgNP-O-(CH₂-CH₂)n-O-CIP interactions, showing OH, NH, and C=O sites); blue and red encased area represent PEG and CIP, respectively; the circle represents the AgNPs; (A) represents –(C=O)-OH-based CIP conjugation, (B) represents piperazinyl NH-based CIP conjugation, and (C) represents (HO-)-C=O-based CIP conjugation.

Figure 3

Space-filling chemical models of the AgNP-PEG-CIP (two methylene units,-CH₂-CH₂, of the AgNP-PEG-CIP, i.e., AgNP-O-(CH₂-CH₂)n-O-CIP)) interactions, showing compacted structures with OH, NH and C=O sites in close conjugations to the PEG unit: (A) –(C=O)-OH-based CIP conjugation, (B) piperazinyl NH-based CIP conjugation, (C) (HO-)-C=O-based CIP conjugation—the AgNPs are omitted from the space-filled models.

Figure 4

Chemically synthesized AgNPs and their conjugates: (A) AgNO₃, (B) synthesized AgNPs, (C) AgNPs-PEG, (D) AgNPs-CIP, (E) AgNPs-PEG-CIP, and (F) Ciprofloxacin.

Figure 5

UV-Visible spectrum of AgNPs, CIP, PEG, and their conjugates.

Figure 6

Fourier-transform infrared (FT-IR) spectra of AgNPs and their conjugates.

Figure 7

X-ray diffraction pattern of AgNPs and their conjugates.

Figure 8

Zeta potentials and dynamic light scattering analyses of AgNPs, AgNPs-PEG, and AgNPs-PEG-CIP.

Figure 9

SEM images (left panels; scale bar 3 µm) and particle size measurements (right panels; scale bar 500 nm). (A) AgNPs, (B) AgNPs-PEG, and (C) AgNPs-PEG-CIP.

Figure 10

EDX spectra for AgNPs, AgNPs-PEG, and AgNPs-PEG-CIP.

Figure 11

TEM images of AgNPs and their conjugates: (A) AgNPs, (B) AgNPs-PEG, and (C) AgNPs-PEG-CIP.

Figure 12

Antioxidant activity of AgNPs, AgNPs-CIP, AgNPs-PEG, and AgNPs-PEG-CIP using the DPPH assay method. Ascorbic acid was used as the positive control.

Figure 13

The synergistic effects of the AgNPs-PEG, AgNPs-CIP, and AgNPs-PEG-CIP on the growth of pathogenic bacteria, compared to CIP and to AgNPs alone.

Figure 14

The anti-biofilm effects of AgNPs and their conjugates at 12.5, 25, 50, and 100 μg mL⁻¹ concentrations by (A) S. aureus, (B) A. baumannii, and (C) S. marcescens.

Figure 15

Minimum inhibitory concentrations (MIC) and minimum bactericidal concentrations (MBC) of the AgNPs and their conjugates against pathogenic bacteria: (A) S. aureus, (B) A. baumannii, and (C) S. marcescens.