A composition including metallic silver nanoparticles is supported on a carrier, wherein the carrier is in the form of particles. The carrier is selected from an inert carrier or an antibiotic. The composition further includes at least one antibiotic in the case the carrier is an inert carrier. A related nanosystem includes a composition having metallic silver nanoparticles or a mixture of silver nanoparticles and at least one antibiotic for use in the treatment of an infection caused by at least one strain of bacteria resistant to at least one antibiotic. Pharmaceutical compositions and methods for the preparation of these compositions and nanosystems are also used for the treatment of bacterial infections.