Green synthesis of Fe3O4/Ag nanocomposite by Spirulina platensis cyanobacteria extract and evaluation of their effect on norA and norB efflux pump genes expression in ciprofloxacin-resistant strain of Staphylococcus aureus

Today, the overuse of antibiotics has led to the emergence of antibioticresistant strains of bacteria, and a worldwide crisis in the battle against them. Accordingly, the discovering, production, and prescribing of new antimicrobial compounds have become one of the most important concerns of researchers. The antibacterial activity of silver nanoparticle, as well as Fe3O4 nanoparticles, had been previously studied and widely described. Synthesis of nanocomposites from the combination of two types of nanoparticles with antibacterial effect increases the performance of both materials. There are several methods for the synthesis of nanoparticles among which, green techniques that refer to the synthesis of metal nanoparticles by natural sources were developed and considered as an eco-friendly and cost-effective alternative for chemical and physical methods. Here, we report the biosynthesis and characterization of Fe3O4/Ag nanocomposites by Spirulina platensis cyanobacteria and their impacts on the expression of efflux pump genes in ciprofloxacin-resistant strains of Staphylococcus aureus. S. aureus is one of the most common pathogens responsible for nosocomial infections that can acquire resistance to antibiotics by different mechanisms including drug extrusion through efflux pumps such as NorA and NorB. The physical properties of biosynthesized nanocomposites measured and confirmed by ultravioletvisible spectroscopy, Fourier-transform infrared spectroscopy, X-ray diffraction, scanning electron microscopy and transmission electron microscopy. Minimum inhibitory concentration (MIC) of ciprofloxacin in antibiotic-resistant S. aureus strains determined in the presence of Fe3O4/Ag nanoparticles by broth microdilution method. The effect of Fe3O4/Ag nanoparticle on the expression of norA and norB genes were evaluated by Real-time PCR. The UV–Visible spectroscopy exhibited the presence of absorbance peak at 390 nm that clearly indicates the formation of Fe3O4/Ag NPs in the solution. SEM and TEM microscopy of biosynthesized Fe3O4/Ag NPs showed a spherical shape with an average size of 10 + 2 nm that are well dispersed with the concentration of 2.3 × 107 particles/mL. XRD patterns are in agreement with the results of electron microscopy and confirmed the crystalline structure of the synthesized Fe3O4/Ag NPs. The results of FT-IR analysis confirmed the stability and biocompatibility of biosynthesized nanoparticles by capping them with biomolecules in the cyanobacterial biomass extract. The MIC values for ciprofloxacin and Fe3O4/Ag NPs were 32 μg/mL and 64 μg/mL, respectively. Moreover, reduction of the antibiotic MIC in the presence of nanoparticles to at least one-quarter of the initial value clearly evidenced synergistic effect of two antibacterial agents to effective inhibition of bacterial growth. In the presence of Fe3O4/Ag NPs,the expression of norA and norB genes were significantly increased that may be the reflection of the bacterial effort for survival. In conclusion, the green synthesized Fe3O4/Ag NPs enhanced the antibacterial effect of ciprofloxacin against ciprofloxacin-resistant S. aureus. Therefore, the Fe3O4/Ag nanocomposites can be used as effective inhibitors of antibiotic resistance in medicine.

کلیدواژه ها:

Antibacterial activity ، Fe3O4/Ag nanocomposite ، Efflux pump ، NorA ، NorB ، Spirulina platensis cyanobacteria