Salmonella Rapidly Regulates Membrane Permeability To Survive Oxidative Stress.

Samuel I. Miller,Lisa A. Reynolds,Franck Duong,Roland Scholz,Joris van der Heijden,Leonard J. Foster,Koshi Imami,Allan Mills,B. Brett Finlay,Wanyin Deng

doi:10.1128/mbio.01238-16

Abstract

ABSTRACTThe 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.

Highlights

The outer membrane (OM) of Gram-negative bacteria provides protection against toxic molecules, including reactive oxygen species (ROS)
Since many antibiotics enter through OM pores, accurate regulation of OM proteins (OMPs) expression lies at the core of antibiotic resistance, which is clearly illustrated by a decreased OM permeability in a majority of the multidrug-resistant bacteria isolated from patients in clinics [5, 6]
It appears that under reducing or mildly oxidizing conditions, when bacteria can grow without extensive damage to intrabacterial components, rapid acquisition of hydrophilic nutrients from the environment requires the wide OmpC pore

Summary

Introduction

The outer membrane (OM) of Gram-negative bacteria provides protection against toxic molecules, including reactive oxygen species (ROS). 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. 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. 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 used this system to accurately measure the real-time influx of H2O2 into living Salmonella enterica serovar Typhimurium bacteria during exposure to ROS and identified regulatory mechanisms that alter OM permeability and ROS sensitivity

Methods

Results

Conclusion