The biosynthesis of metal nanoparticles is an expanding research area due to the potential applications for emerging ecofriendly science. The present study proved a rapid and extracellular biosynthesis of silver nanoparticles (AgNPs) by a fungus, Fusarium moniliforme, isolated from infected onion. Upon addition of the silver ion into the flask containing the mycelial mat, the color of the medium changed to brown, typical of the AgNPs. The AgNPs showed maximum absorbance at 420 nm on ultraviolet-visible spectra. The transmission electron micrograph revealed the formation of AgNPs with an average size of about 50-100 nm. The presence of proteins was identified by Fourier transform-infrared spectroscopy. Combination between AgNPs and ciprofloxacin was evaluated for their antimicrobial activities, and the antibacterial activity of ciprofloxacin was increased in the presence of AgNPs against some food borne bacteria i.e. Bacillus subtilis, Staphylococcus aureus, Escherichia coli and Salmonella typhi.