The effect of a bacteriocin of Enterococcus on the oxidative metabolism of sensitive bacteria was investigated through the detection of oxidative stress by chemiluminescence (CL). The bacteriocin named EntB was purified to study the action on Staphylococcus aureus isolated from cosmetic. Chromatographic separation of EntB indicated different states of oligomerization with molecular weights multiple of 12,000 Da monomeric form. The monomer purified by ion exchange was studied in its capacity to affect the oxidative metabolism of S. aureus, which showed increase of anion superoxide (O-2(-)) when incubated with EntB. This effect was compared to the action of EntB on leukocytes as an assay of toxicity. EntB did not generate significant oxidative stress in leukocytes. Pyoverdin, a leukotoxic pigment of Pseudomonasfluorescens, was taken as reference, and it was found that this pigment caused similar oxidative stress to EntB in S. aureus; however, pyoverdin generated high production of anion superoxide (O-2(-)) in leukocytes, while EntB did not increase the level of O-2(-) (C) 2003 Published by Elsevier Inc.