Oxidation of the Guanine Nucleotide Pool Underlies Cell Death by Bactericidal Antibiotics

Department of Biology, Massachusetts Institute of Technology, Cambridge, MA 02139, USA.
Science (Impact Factor: 33.61). 04/2012; 336(6079):315-9. DOI: 10.1126/science.1219192
Source: PubMed


A detailed understanding of the mechanisms that underlie antibiotic killing is important for the derivation of new classes
of antibiotics and clinically useful adjuvants for current antimicrobial therapies. Our efforts to understand why DinB (DNA
polymerase IV) overproduction is cytotoxic to Escherichia coli led to the unexpected insight that oxidation of guanine to 8-oxo-guanine in the nucleotide pool underlies much of the cell
death caused by both DinB overproduction and bactericidal antibiotics. We propose a model in which the cytotoxicity of beta-lactams
and quinolones predominantly results from lethal double-strand DNA breaks caused by incomplete repair of closely spaced 8-oxo-deoxyguanosine
lesions, whereas the cytotoxicity of aminoglycosides might additionally result from mistranslation due to the incorporation
of 8-oxo-guanine into newly synthesized RNAs.

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    • "Bactericidal drugs kill bacteria partly by induction of ROS formation (Kohanski et al., 2007; Foti et al., 2012). The detection of ROS in treated B. cereus is a common signal in cellular death pathways (Kohanski et al., 2007). "
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    • "Norfloxacin is a synthetic antibacterial agent and a broad-spectrum antibiotic that is active against both gram-positive and gram-negative bacteria . Norfloxacin induces accumulation of ROS, highly destructive molecules that appear to oxidize DNA and lethal double-strand DNA breaks caused by incomplete repair can contribute to cell death in bacteria (Kohanski et al. 2007; Foti et al. 2012). The assay results showed that nano-Ag has antibacterial activity. "
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    • "Moreover, a recent work identified a significant decrease in mutation rates in MMR deficient, laboratory evolved E. coli lines associated with enhanced ROS detoxification (Turrientes et al. 2013). The weak effect of deactivated error-prone DNA repair in ÁdinBÁfur and ÁdinBÁumuDCÁfur mutants indicates that the majority of resistance mutations is formed by direct oxidation of DNA and not by incorporation of oxidized nucleotides through error-prone DNA polymerases (Foti et al. 2012). Indeed, we failed to find significant differences in the spectra of accumulated adaptive mutations between WT and Áfur populations (supplementary fig. "
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    ABSTRACT: Evolution of antibiotic resistance in microbes is frequently achieved by acquisition of spontaneous mutations during antimicrobial therapy. Here, we demonstrate that inactivation of a central transcriptional regulator of iron homeostasis (Fur) facilitates laboratory evolution of ciprofloxacin resistance in Escherichia coli. To decipher the underlying molecular mechanisms, we first performed a global transcriptome analysis and demonstrated that the set of genes regulated by Fur changes substantially in response to antibiotic treatment. We hypothesized that the impact of Fur on evolvability under antibiotic pressure is due to the elevated intracellular concentration of free iron and the consequent enhancement of oxidative damage-induced mutagenesis. In agreement with expectations, overexpression of iron storage proteins, inhibition of iron transport, or anaerobic conditions drastically suppressed the evolution of resistance, whereas inhibition of the SOS response-mediated mutagenesis had only a minor effect. Finally, we provide evidence that a cell permeable iron chelator inhibits the evolution of resistance. In sum, our work revealed the central role of iron metabolism in the de novo evolution of antibiotic resistance, a pattern that could influence the development of novel antimicrobial strategies.
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