title: New aspect of the synergistic antibacterial action of ampicillin and gentamicin.
abstract: A new aspect in the action of ampicillin and gentamicin was detected in Enterococcus faecalis. Reactive oxygen species (ROS) increased in sensitive strains during treatment with each antibiotic up to a certain concentration of antibiotic, above which ROS diminished as a consequence of oxidative stress. Tiron, a scavenger of the superoxide anion O(2)(-), counteracted the effect of the generated ROS. The oxidative stress was a consequence of an increase in ROS in the cytoplasm of bacteria, as observed by the nitroblue tetrazolium reaction. The viability of sensitive strains was significantly reduced at concentrations of antibiotics that increased the ROS, and this increment was parallel to the bactericidal effect. Sensitive E. faecalis strains showed an immediate increase of ATP in the presence of both antibiotics, thus an energy-dependent process had been triggered, indicating a bacterial reaction against the stress. The combination of both antibiotics augmented the effect of ROS, which helps to explain the synergism between ampicillin and gentamicin.
authors: Departamento de Farmacia, Facultad de Ciencias Químicas, Universidad Nacional de Córdoba, Haya de la Torre y Medina Allende, Ciudad Universitaria, 5000 Córdoba, Argentina.
authors: A I
authors: AI
authors: Barnes
authors: I L
authors: IL
authors: Herrero
authors: I
authors: I
authors: Albesa
mesh_terms: D000667:Ampicillin / Q000494:pharmacology*; D000900:Anti-Bacterial Agents / Q000494:pharmacology*; D004357:Drug Synergism; D013293:Enterococcus faecalis / Q000187:drug effects* / Q000201:enzymology / Q000378:metabolism; D005839:Gentamicins / Q000494:pharmacology*; D018384:Oxidative Stress / Q000187:drug effects* / Q000502:physiology; D010100:Oxygen / Q000378:metabolism*; D017382:Reactive Oxygen Species / Q000378:metabolism*
chemical_list: D000900:Anti-Bacterial Agents; D005839:Gentamicins; D017382:Reactive Oxygen Species; D000667:Ampicillin; D010100:Oxygen