Bifunctional nano-Ag3PO4 with capabilities of enhancing ceftazidime for sterilization and removing residues

Abstract

Since the efficacy of antibiotics towards bacteria is decreasing over time, the rising of antibiotic emission has become an increasingly grave issue. In this study, we proposed an integrated antibacterial nanotechnology without pollution residues, which synergistically enhances the antibacterial activity of ceftazidime by using the inorganic nano-Ag₃PO₄, and subsequently removes drug residues by photocatalysis. Ag₃PO₄ were synthesized using a simple ion-exchange method without any reducing agent or protectant. The combined antibacterial activity of Ag₃PO₄ and 22 kinds of antibiotics against Escherichia coli was first studied. The results showed that Ag₃PO₄ and ceftazidime exhibited the best synergistic effect. Next, the synergy mechanism was proposed, the non-chemical bond forces between Ag₃PO₄ and ceftazidime was determined by zeta potential analyzer, X-ray photoelectron spectroscopy (XPS) and infrared spectroscopy (IR). The interaction between antimicrobials and bacteria was further demonstrated by surface plasma resonance spectroscopy (SPR), scanning electron microscopy (SEM) and propidium iodide (PI) staining. In addition, the production of reactive oxygen species (ROS), the induction of oxidative stress and dissolution of silver ions in Ag₃PO₄ were studied and found out that only under light, could the ROS be generated. In conclusion, the synergistic effect of Ag₃PO₄ and ceftazidime is responsible for the joint destruction of cell wall.

Fig. 1. XRD pattern of Ag₃PO₄.

Fig. 2. SEM images of Ag₃PO₄.

Fig. 3. XPS images of Ag₃PO₄ with ceftazidime.

Fig. 4. Infrared spectra of Ag₃PO₄ with ceftazidime.

Fig. 5. SPR curves of Ag₃PO₄, Ag₃PO₄–CAZ with E. coli.

Fig. 6. SEM images of E. coli treated by (a and b) negative control, (c and d) 10 mg L⁻¹ Ag₃PO₄, (e and f) 10 mg L⁻¹ ceftazidime, (g and h) 10 mg L⁻¹ Ag₃PO₄ and 10 mg L⁻¹ ceftazidime, (i and j) 100 mg L⁻¹ Ag₃PO₄, (k and l) 100 mg L⁻¹ ceftazidime, (m and n) 100 mg L⁻¹ Ag₃PO₄ and 100 mg L⁻¹ ceftazidime, (o and p) 1000 mg L⁻¹ Ag₃PO₄, (q and r) 1000 mg L⁻¹ ceftazidime, (s and t) 1000 mg L⁻¹ Ag₃PO₄ and 1000 mg L⁻¹ ceftazidime.

Fig. 7. Permeability of bacterial cell membrane probed by PI (concentration units are mg L⁻¹).

Fig. 8. EPR images of Ag₃PO₄ in the dark and light.

Fig. 9. Intracellular reactive oxygen species (ROS) probed by DCFH-DA (concentration units are mg L⁻¹).

Fig. 10. The dissolution of Ag₃PO₄ in LB broth with or without ceftazidime.

Fig. 11. The photocatalytic degradation of ceftazidime by Ag₃PO₄ under simulated solar radiation.

Fig. 12. Schematic drawing of the synergistic mechanisms of Ag₃PO₄ with ceftazidime against Escherichia coli.