The invention relates to the use of stable atomic quantum clusters (AQC) with antimicrobial activity. The stable AQCs include at least 500 metal atoms (Mn, n<500), the metals being selected from among Au, Ag, Co, Cu, Pt, Fe, Cr, Pd, Ni, Rh, Pb or bi- or multi-metallic combinations thereof. Said AQCs are used as antimicrobial agents, antifungal agents and biocides at concentrations of the order of between 1 nM and 100 nM or more in relation to atoms of the corresponding metal. The antimicrobial activity is specific to both the type of metal and size of cluster used.