Biosynthesis of NiFe2 O4 @Ag Nanocomposite and Assessment of Its Effect on Expression of norA Gene in Staphylococcus aureus.

Activity of norA efflux pump has been known as a resistance mechanism to antibiotics like ciprofloxacin in Staphylococcus aureus. This study was carried out to assess the effect of biosynthesized NiFe2 O4 @Ag nanocomposite on expression of norA gene in Staphylococcus aureus. In this experimental study, 30 clinical samples were collected from patients hospitalized at different hospitals in Guilan Province, Iran. Then, clinical isolates of S. aureus were identified by standard microbiological tests. Antimicrobial susceptibility tests of clinical and standard strains of S. aureus were done by disk diffusion method according to CLSI guideline. Fourier transform infrared spectroscopy (FT-IR) was used to analyze the various functional groups present in the biosynthesized NiFe2 O4 @Ag nanocomposite. This analysis confirmed the formation of alga proteins coated on magnetite nanocomposite. X-ray diffraction (XRD) verified the crystalline structure of NiFe2 O4 @Ag and the deposition of silver on the surface of NiFe2 O4 . Energy dispersive X-ray mapping (EDX-map) analysis confirmed the existence of Ag, Ni, Fe and O in the final product. Scanning electron microscopy (SEM) confirmed that the nanocomposites were spherical in shape and Transmission electron microscopy (TEM) results revealed that the NiFe2 O4 @Ag had the particle size about 100 nm. Antibacterial activity of NiFe2 O4 @Ag alone and combined with ciprofloxacin was evaluated using the disk assay method, and minimum inhibitory concentration (MIC) by broth dilution method. Afterwards, the expression of norA efflux pump gene with and without of NiFe2 O4 @Ag nanocomposite and ciprofloxacin was evaluated by Real-Time PCR. Real-Time PCR results demonstrated that the expression of norA gene in the strains exposed to both NiFe2 O4 @Ag nanocomposite (1/4 MIC) and ciprofloxacin (1/8 MIC) significantly reduced in comparison to untreated strains. This study reveals that, when NiFe2 O4 @Ag nanocomposite is combined with ciprofloxacin, the inhibitory effect of ciprofloxacin increases against growth of S. aureus. Therefore, NiFe2 O4 @Ag nanocomposite can be considered as an effective factor to decrease the growth of S. aureus along with ciprofloxacin.