Antibacterial mechanism of bifidocin A, a novel broad-spectrum bacteriocin produced by Bifidobacterium animalis BB04

Bifidocin A, a novel broad-spectrum bacteriocin produced by Bffidobacterium animalis BB04, was isolated from the feces of a healthy centenarian. To understand the mechanism of the antibacterial action of bifidocin A against gram-negative bacteria, its effects at a minimum inhibitory concentration on cell morphology, intracellular organization, membrane permeability, membrane integrity, and membrane proton motive force (PMF) of Escherichia coli 1.90 were investigated. Scanning and transmission electron microscopy analyses showed that bifidocin A induced alterations in the morphology and intracellular organization of E. coil cells. The intracellular organization was more susceptible to changes induced by bifidocin A than the morphology. Bifidocin A treatment caused the leakage of IC+ and inorganic phosphate, the release of ATP and UV-absorbing materials, and a collapse of the transmembrane electrical potential and pH gradient in E. coil cells. Confocal laser scanning microscopy images showed that E. coil cells treated with bifidocin A took up propidium iodide. These results suggested that the mechanism of action bifidocin A against E. coil involved dissipation of the PMF of the cytoplasmic membrane, an increase in membrane permeability, pore formation in the cell membrane, a change in membrane integrity, and complete cell disintegration. (C) 2015 Elsevier Ltd. All rights reserved.