Rodrigo S. Galhardo, Alexandro Rodríguez-Rojas, Ana I. Rodríguez-Rosado, Coloma Costas, Estela Y. Valencia, Jerónimo Rodríguez-Beltrán, Jesús Blázquez, Ministerio de Economía y Competitividad (España), Instituto de Salud Carlos III, Conselho Nacional de Desenvolvimento Científico e Tecnológico (Brasil), and Fundação de Amparo à Pesquisa do Estado de São Paulo
[Background]: Fluoroquinolones such as ciprofloxacin induce the mutagenic SOS response and increase the levels of intracellular reactive oxygen species (ROS). Both the SOS response and ROS increase bacterial mutagenesis, fuelling the emergence of resistant mutants during antibiotic treatment. Recently, there has been growing interest in developing new drugs able to diminish the mutagenic effect of antibiotics by modulating ROS production and the SOS response., [Objectives]: To test whether physiological concentrations of N-acetylcysteine, a clinically safe antioxidant drug currently used in human therapy, is able to reduce ROS production, SOS induction and mutagenesis in ciprofloxacin-treated bacteria without affecting antibiotic activity., [Methods]: The Escherichia coli strain IBDS1 and its isogenic mutant deprived of SOS mutagenesis (TLS−) were treated with different concentrations of ciprofloxacin, N-acetylcysteine or both drugs in combination. Relevant parameters such as MICs, growth rates, ROS production, SOS induction, filamentation and antibiotic-induced mutation rates were evaluated., [Results]: Treatment with N-acetylcysteine reduced intracellular ROS levels (by ∼40%), as well as SOS induction (by up to 75%) and bacterial filamentation caused by subinhibitory concentrations of ciprofloxacin, without affecting ciprofloxacin antibacterial activity. Remarkably, N-acetylcysteine completely abolished SOS-mediated mutagenesis., [Conclusions]: Collectively, our data strongly support the notion that ROS are a key factor in antibiotic-induced SOS mutagenesis and open the possibility of using N-acetylcysteine in combination with antibiotic therapy to hinder the development of antibiotic resistance., This study was funded by the Spanish Plan Nacional de I!D!i 2013- 2016; grant SAF2015-72793-EXP (AEI/FEDER, UE) and the Instituto de Salud Carlos III (ISCIII), Subdireccio´n General de Redes y Centros de Investigacio´n Cooperativa, Ministerio de Economı´a, Industria y Competitividad; grant FIS PI17/00159 (ISCIII/FEDER, UE) and Spanish Network for Research in Infectious Diseases; grant REIPI RD16/0016/ 0009, cofinanced by the European Development Regional Fund ‘A Way to Achieve Europe’ and by Operative Program IntelligentGrowth 2014- 2020. E. Y. V. was funded by a postdoctoral fellowship from Conselho Nacional de Desenvolvimento Cientı´fico e Tecnolo´gico (CNPq), Brazil (grant 236914/2012–0). R. S. G. was supported by Fundac¸ao de Amparo ~ a` Pesquisa do Estado de Sao Paulo (FAPESP), Brazil (grant 2014/15982–6) ~ and CNPq, Brazil (grant 407259/2013–9). J. R.-B. is a recipient of a Juan de la Cierva Fellowship, Ministerio de Economı´a Industria y Competitividad (FJCI-2016–30019). J. B. was supported by: the Spanish Plan Nacional de I ! D!i 2013–2016 and the Instituto de Salud Carlos III, Subdireccio´n General de Redes y Centros de Investigacio´n Cooperativa, Ministerio de Economı´a, Industria y Competitividad, Spanish Network for Research in Infectious Diseases; grant REIPI RD16/0016/ 0009, cofinanced by the European Development Regional Fund ‘A Way to Achieve Europe’ and by Operative Program IntelligentGrowth 2014– 2020; and grants FIS PI17/00159 (ISCIII/FEDER, UE) and SAF2015- 72793-EXP (AEI/FEDER, UE).