The inhibitory activities of known microcins were evaluated against some diarrheagenic Escherichia coli strains. Some antibacterial properties of microcin J25, the most active one, were studied. A rapid two-step purification was performed. The MIC and the minimum bactericidal concentration of J25 against E. coli O157:H7 were 1 and 100 μg ml ⁻¹ , respectively. A 10 ⁴ -CFU ml ⁻¹ contamination by this strain was destroyed in milk and meat extract by 6.25 μg of J25 ml ⁻¹ and in half-diluted egg yolk by 50 μg of J25 ml ⁻¹ .