Polyamine-Mediated Resistance of Uropathogenic Escherichia coli to Nitrosative Stress

Abstract

During the course of a urinary tract infection, substantial levels of nitric oxide and reactive nitrogen intermediates are generated. We have found that many uropathogenic strains of Escherichia coli display far greater resistance to nitrosative stress than the K-12 reference strain MG1655. By selecting and screening for uropathogenic E. coli transposon mutants that are unable to grow in the presence of acidified nitrite, the cadC gene product was identified as a key facilitator of nitrosative stress resistance. Mutation of cadC, or its transcriptional targets cadA and cadB, results in loss of significant production of the polyamine cadaverine and increased sensitivity to acidified nitrite. Exogenous addition of cadaverine or other polyamines rescues growth of cad mutants under nitrosative stress. In wild-type cells, the concentration of cadaverine produced per cell is substantially increased by exposure to acidified nitrite. The mechanism behind polyamine-mediated rescue from nitrosative stress is unclear, but it is not attributable solely to chemical quenching of reactive nitrogen species or reduction in mutation frequency.Along with its roles in neurotransmission, vasodilation, cell adhesion, and platelet inhibition, nitric oxide (NO) is also a key player in innate immunity. NO is formed by the action of nitric oxide synthases (NOS), which are induced and activated during the course of infections caused by many different pathogens. NO may then be converted to a variety of other damaging reactive nitrogen intermediates (RNIs) such as peroxynitrite and nitrosothiols. These RNIs can inflict extensive damage on the nucleic acids, proteins, and lipids of invading microbes. Thiols, amines, aromatic residues, heme groups, and iron-sulfur clusters are particularly susceptible to attack (9, 10). NOS activity has been shown to be crucial in control of pathogen load in numerous infections, particularly Salmonella, Leishmania, and Listeria spp. and mycobacteria (9).Other infections which may be influenced by RNIs are those elicited by strains of uropathogenic Escherichia coli (UPEC). These bacteria are the primary causative agents of urinary tract infections, including both bladder and kidney infections (3). Within hours of initiation of a bladder infection, levels of nitrite in the urine increase threefold (24), and eventually gaseous levels of NO within the bladder increase 30-to 50-fold over uninfected controls (17). Much of this increase is likely due to the action of endothelial (e) NOS in the bladder, which has been shown to be upregulated and activated by intraperitoneal injection of E. coli lipopolysaccharide (14). The bacteria themselves, which can produce NO through nitrite reductases under conditions of low oxygen tension (7), may also contribute to the high levels of RNIs in an infected bladder. Like mycobacteria and several other pathogens that are known to be kept in check by RNIs, UPEC can persist long-term within a host as an intracellular pathogen and may lie in wait in quiescent reservoirs between recur...

Inactivation of Host Akt/Protein Kinase B Signaling by Bacterial Pore-forming Toxins

“…In response to lipopolysaccharide, eNOS within the bladder is rapidly induced and activated, presumably as part of the host defense against UTIs (Kang et al, 2004). Akt-dependent phosphorylation and subsequent activation of eNOS stimulates the production of nitric oxide, which can have considerable bacteriostatic effects on UPEC (Dimmeler et al, 1999;Fulton et al, 1999;Bower and Mulvey, 2006). Analogously, Akt-mediated phosphorylation of p47 phox facilitates the generation of reactive oxygen species during respiratory burst by neutrophils in response to bacterial pathogens such as UPEC (Chen et al, 2003b;Hoyal et al, 2003;Bedard and Krause, 2007).…”

Surface-Localized Spermidine Protects the Pseudomonas aeruginosa Outer Membrane from Antibiotic Treatment and Oxidative Stress

“…Microscopy was used to confirm the membrane localization of C 11 -BODIPY 581/591 , which is therefore a targeted indicator of damage to outer membrane lipids. A previous report implicated cadaverine in protecting E. coli from nitrosative stress, although the mechanism of protection was unclear (6). The presence of polyamines on the cell surface may act to scavenge ROS (16), thereby limiting the damage to the lipids buried in the membrane.…”

The porin and the permeating antibiotic: a selective diffusion barrier in Gram-negative bacteria

“…In addition, cadaverine has been shown to reduce ampicillin and cephaloridine susceptibility in E. coli by promoting an inhibition of ionic flux through cationic porins 85,88 . Thus, inhibition of porin transport by excreted cadaverine might represent a mechanism that provides bacterial cells with the ability to survive acid stress and nitrosative stress [89][90][91] . In the presence of antibiotics that use porins to cross the membrane barrier, cadaverine might play the part of pore modulator and reduce the penetration rate of these antibacterial agents.…”