Iron Homeostasis Affects Antibiotic-mediated Cell Death in Pseudomonas Species

Abstract

Antibiotics can induce cell death via a variety of action modes, including the inhibition of transcription, ribosomal function, and cell wall biosynthesis. In this study, we demonstrated directly that iron availability is important to the action of antibiotics, and the ferric reductases of Pseudomonas putida and Pseudomonas aeruginosa could accelerate antibiotic-mediated cell death by promoting the Fenton reaction. The modulation of reduced nicotinamide-adenine dinucleotide (NADH) levels and iron chelation affected the actions of antibiotics. Interestingly, the deletion of the ferric reductase gene confers more antibiotic resistance upon cells, and its overexpression accelerates antibiotic-mediated cell death. The results of transcriptome analysis showed that both Pseudomonas species induce many oxidative stress genes under antibiotic conditions, which could not be observed in ferric reductase mutants. Our results indicate that iron homeostasis is crucial for bacterial cell survival under antibiotics and should constitute a significant target for boosting the action of antibiotics.

The Fluoroquinolone Levofloxacin Triggers the Transcriptional Activation of Iron Transport Genes That Contribute to Cell Death in Streptococcus pneumoniae

“…This result agrees with a recent proposal suggesting that, following gyrase poisoning, hydroxyl radical formation utilizing internal iron and the Fenton reaction (33) is generated and contributes to cell killing by FQs (34) as well as by other bactericidal antibiotics (35,36). In this mechanism, proposed for Enterobacteriaceae (35,37), the primary drug interactions stimulate oxidation of NADH via the electron transport chain that is dependent on the tricarboxylic acid cycle. Hyperactivation of the electron transport chain stimulates superoxide formation.…”

The Stringent Response Controls Catalases in Pseudomonas aeruginosa and Is Required for Hydrogen Peroxide and Antibiotic Tolerance

“…Recent studies suggest that bactericidal antibiotics kill bacteria through oxidative-stress-induced damage, in particular through the formation of highly reactive hydroxyl radicals (34)(35)(36)69). Consistent with this model, the E. coli oxyR mutant is more susceptible to aminoglycoside killing (70).…”

“…Since recent studies suggest that oxidative-stress pathways contribute to bacterial cell death caused by bactericidal antibiotics (34)(35)(36)(37)(38), we hypothesized that robust antioxidant defenses are required for antibiotic tolerance. Our initial studies showed that the ⌬SR (⌬relA ⌬spoT) mutant had decreased superoxide dismutase and catalase activities and was more susceptible to oxidants than wildtype P. aeruginosa (33).…”

Generation of reactive oxygen species by lethal attacks from competing microbes

“…ROS can cause lethal damage to DNA, lipid, and proteins (19,20) and thus can contribute to cell death in combination with the deleterious effects of antibiotics on their primary targets. The idea that antibiotics kill bacterial cells, in part, through the action of ROS has been supported by a number of follow-up studies (18,(21)(22)(23) but has also been challenged by others as a result of observations contradictory to a model where ROS is the sole mediator of antibiotic lethality (24)(25)(26). These observations include the fact that antibiotics kill under anaerobic conditions, oxidation of the hydroxyphenyl fluorescein fluorescence dye used to measure ROS levels is nonspecific, and the extracellular level of H 2 O 2 is not elevated by antibiotic treatment (24,26).…”