Salmonella Rapidly Regulates Membrane Permeability To Survive Oxidative Stress

The outer membrane (OM) of Gram-negative bacteria provides protection against toxic molecules, including reactive oxygen species (ROS). Decreased OM permeability can promote bacterial survival under harsh circumstances and protects against antibiotics. To better understand the regulation of OM permeability, we studied the real-time influx of hydrogen peroxide in Salmonella bacteria and discovered two novel mechanisms by which they rapidly control OM permeability. We found that pores in two major OM proteins, OmpA and OmpC, could be rapidly opened or closed when oxidative stress is encountered and that the underlying mechanisms rely on the formation of disulfide bonds in the periplasmic domain of OmpA and TrxA, respectively. Additionally, we found that a Salmonella mutant showing increased OM permeability was killed more effectively by treatment with antibiotics. Together, these results demonstrate that Gram-negative bacteria regulate the influx of ROS for defense against oxidative stress and reveal novel targets that can be therapeutically targeted to increase bacterial killing by conventional antibiotics. IMPORTANCE Pathogenic bacteria have evolved ways to circumvent inflammatory immune responses. A decrease in bacterial outer membrane permeability during infection helps protect bacteria from toxic molecules produced by the host immune system and allows for effective colonization of the host. In this report, we reveal molecular mechanisms that rapidly alter outer membrane pores and their permeability in response to hydrogen peroxide and oxidative stress. These mechanisms are the first examples of pores that are rapidly opened or closed in response to reactive oxygen species. Moreover, one of these mechanisms can be targeted to artificially increase membrane permeability and thereby increase bacterial killing by the antibiotic cefotaxime during in vitro experiments and in a mouse model of infection. We envision that a better understanding of the regulation of membrane permeability will lead to new targets and treatment options for multidrug-resistant infections.