Superoxide-Mediated Protection of Escherichia coli from Antimicrobials

Antimicrobial lethality is promoted by reactive oxygen species (ROS), such as superoxide, peroxide, and hydroxyl radical. Pretreatment with subinhibitory concentrations of plumbagin or paraquat, metabolic generators of superoxide, paradoxically reduced killing for oxolinic acid, kanamycin, and ampicillin. These pretreatments also reduced an oxolinic acid-mediated ROS surge. Defects in SoxS MarA or AcrB eliminated plumbagin- and paraquat-mediated MIC increases but maintained protection from killing. Thus, superoxide has both protective and detrimental roles in response to antimicrobial stress.