Abstract: Silver nanoparticles (AgNPs) have been shown great interest because of their potential antibacterial effect. Recently, this has been increased due to resistance in some pathogenic bacteria strains to conventional antibiotics, which has initiated new studies to search for more effective treatments against resistant microorganisms. For these reasons, AgNPs have become an important approach for applications in nanobiotechnology in the development of antibiotic treatment of different bacterial infections. This study was aimed at synthesizing AgNPs using cysteine as a reducer agent and cetyl-tri-methyl-ammonium bromide as a stabilizer in order to obtain more efficient treatment against the pathogen bacteria Escherichia coli O157:H7. These AgNPs were characterized through UV-Vis spectroscopy, transmission electron microscopy, and dynamic light scattering. From these analyses, formation of spherical nanoparticles with an average size of 55 nm was confirmed. Finally, minimal inhibitory concentration (MIC) and minimal bactericide concentration (MBC) of these AgNPs against pathogenic strains E. coli O157:H7 and methicillin-resistant Staphylococcus aureus (MRSA) were determined in both solid and liquid media. MIC and MBC values were around 0.25 µg/mL and 1 µg/mL, respectively. These parameters were comparable to those reported in the literature and were even more effective than other synthesized AgNPs. Keywords: nanomaterials, antibacterial activity, minimal inhibitory concentration, MIC, minimal bactericide concentration, MBC