Abstract: An antimicrobial agent comprising a selenium nanoparticle (SeNP) core and one or more superficially located antimicrobial peptide/s (AMP). The or each AMP may comprise an excess of positively charged amino acids compared to negatively charged amino acids and the AMP may comprise peptides from classes selected from polylysine, such as ?-poly-L-lysine (?-PL), polyarginine, aurein, ovispirin, melittin, magainin, cecropin, andropin, moricin, ceratotoxin, melittin, magainin, dermaseptin, bombinin, brevinin, esculentins, buforin, cathelicidin, abaecin, apidaecin, prophenin and indolicidin. Products comprising such agents, methods of producing the agents and methods of killing or retarding growth of microorganisms exposed to the agents are also disclosed.