Silver nanoparticles (Ag NPs) have drawn a lot of interest because of their antibacterial activity. However, their synthesis by chemical methods is potentially harmful; this is the reason why the use of plant extract for synthesis constitutes a simple, effective and safe alternative solution.

In this work, Ag NPs were synthesized by the precipitation method; silver nitrate was used as precursor and the extract of Rosmarinus officinalis was used as a reducing as well as capping agent.

They were characterized using X-ray diffraction DRX, UV-visible spectrometry and Fourier-transform infrared spectroscopy (FTIR), and they were also examined for their antimicrobial properties by using the agar diffusion method against gram-negative and gram-positive bacteria.

XRD analysis confirms the crystalline nature of the NPs, with a face-centered cubic (fcc) structure, and reveals that the average crystallite sizes of the Ag NPs are 30nm.

The UV-visible spectrum showed absorption peaks at 220-360 which revealed the presence of functional groups (phenolics, flavonoids, tannins…), and FTIR analysis confirmed their existence and that these biomolecule compounds were not only responsible for the reduction but also the capping of Ag NPs.

Ag NPs exhibited antibacterial activity against both bacteria (gram-negative strain of E. coli BLSE, K. pneumoniae carb-, and gram-positive strain of E. fecalis ATCC292112, S. aureus ATCC25923) withlarge zones of inhibition, respectively (50.7mm, 10.34mm, 17.87 mm, 10.72mm)

The present study showed that the extract of Rosmarinus officinalis can be used as reducing and capping agent to synthesize Ag NPs that present a highly bactericidal effect.