The present invention provides compositions and methods for reducing microbial contamination or infection in plants, animals, fabrics, and products therefrom. The present invention also provides compositions and methods for reducing human infections. In particular, it provides solid magnetic nanoparticles comprising bacteriostatic, bactericidal, fungistatic, or fungicidal enzymes in one component, and substrates for the enzymes in another component. The compositions are dormant and become active upon exposure to hydration and oxygen.