Evolution of antibiotic resistance is a world health crisis, fueled by new mutations. Drugs to slow mutagenesis could, as cotherapies, prolong the shelf-life of antibiotics, yet evolution-slowing drugs and drug targets have been underexplored and ineffective. Here, we used a network-based strategy to identify drugs that block hubs of fluoroquinolone antibiotic-induced mutagenesis. We identify a U.S. Food and Drug Administration– and European Medicines Agency–approved drug, dequalinium chloride (DEQ), that inhibits activation of the Escherichia coli general stress response, which promotes ciprofloxacin-induced (stress-induced) mutagenic DNA break repair. We uncover the step in the pathway inhibited: activation of the upstream “stringent” starvation stress response, and find that DEQ slows evolution without favoring proliferation of DEQ-resistant mutants. Furthermore, we demonstrate stress-induced mutagenesis during mouse infections and its inhibition by DEQ. Our work provides a proof-of-concept strategy for drugs to slow evolution in bacteria and generally.

Pseudomonas aeruginosa is a major cause of nosocomial infections and the leading cause of chronic lung infections in cystic fibrosis and chronic obstructive pulmonary disease patients. Antibiotic treatment remains challenging because P. aeruginosa is resistant to high concentrations of antibiotics and has a remarkable ability to acquire mutations conferring resistance to multiple groups of antimicrobial agents. Here we report that when P. aeruginosa is plated on ciprofloxacin (cipro) plates, the majority of cipro-resistant (ciproR) colonies observed at and after 48 h of incubation carry mutations in genes related to the Stringent Response (SR). Mutations in one of the major SR components, spoT, were present in approximately 40% of the ciproR isolates. Compared to the wild-type strain, most of these isolates had decreased growth rate, longer lag phase and altered intracellular ppGpp content. Also, 75% of all sequenced mutations were insertions and deletions, with short deletions being the most frequently occurring mutation type. We present evidence that most of the observed mutations are induced on the selective plates in a subpopulation of cells that are not instantly killed by cipro. Our results suggests that the SR may be an important contributor to antibiotic resistance acquisition in P. aeruginosa.

Pseudomonas aeruginosa is considered a priority pathogen by the World Health Organization due to its resistance to antibiotics. Isolates resistant to ciprofloxacin (CPFX), a bactericide commonly used against P. aeruginosa, usually carry the mutations T83I or D87N in the GyrA subunit of the DNA gyrase. Yet, the molecular mechanisms by which these mutations confer CPFX-resistance to P. aeruginosa are unknown. Here we solved the crystal structure of the P. aeruginosa gyrase catalytic cleavage core and used it to carry out molecular dynamic (MD) simulations of CPFX-gyrase binding in the wild-type as well as the T83I and the D87N mutant systems. Our results show that DNA plays the most prominent stabilizing role once CPFX is bound, with relatively minor contributions from Thr83 or Asp87. Interestingly, we found a solvent cavity adjacent to these residues that may provide CPFX access to the active site. Interaction energy analysis using Umbrella Sampling indicates that Thr83 and Asp87 may influence CPFX trajectory during binding. In the mutant systems, the repulsive potential increases at the cavity site, which may hinder CPFX accessing the binding site. These results shed light on P. aeruginosa resistance to CPFX and may help provide a methodology to identify new therapeutic agents to target fluoroquinolone resistant bacteria.

Pseudomonas aeruginosa is considered a priority pathogen by the World Health Organization due to its resistance to antibiotics. Isolates resistant to ciprofloxacin (CPFX), a bactericide commonly used against P. aeruginosa , usually carry the mutations T83I or D87N in the GyrA subunit of the DNA gyrase. Yet, the molecular mechanisms by which these mutations confer CPFX-resistance to P. aeruginosa are unknown. Here we solved the crystal structure of the P. aeruginosa gyrase catalytic cleavage core and used it to carry out molecular dynamic (MD) simulations of CPFX-gyrase binding in the wild-type as well as the T83I and the D87N mutant systems. Our results show that DNA plays the most prominent role in maintaining the CPFX-bound conformation, with no appreciable contributions from Thr83 or Asp87. Interestingly, we found a solvent cavity adjacent to these residues that may provide CPFX access to the active site. Interaction energy analysis using Umbrella Sampling indicates that Thr83 and Asp87 may influence CPFX trajectory during binding. In the mutant systems, the attractive potential decreases, which may hinder CPFX accessing the binding site. These results shed light on P. aeruginosa resistance to CPFX and may help provide a methodology to identify new therapeutic agents to target fluoroquinolone resistant bacteria. Graphical abstract caption: Molecular dynamic positioning of ciprofloxacin (CPFX) from the cavity site (green) to the bound inhibition site (magenta) suggests that mutations T83I and D87N, conferring CPFX resistance to the P. aeruginosa gyrase, may have an influence on the ability of CPFX to access the binding site. Protein is shown in cyan, DNA backbone in orange, and DNA bases in gradient from cyan to blue.

Redox stress induces DNA mutations that contribute to chronic conditions affecting human health and to the emergence of antibiotic resistance. Yet, the impact of redox stress-induced mutagenesis remains difficult to decipher because redox agents are diverse and produce hard-to-detect mutational outcomes. Single-stranded DNA (ssDNA) provides a useful tool for studying mutagenic effects of redox agents, as it is particularly susceptible to damage and cannot be repaired by most DNA repair pathways. Here, we established a protocol to investigate redox stress-induced mutagenesis based on the Escherichia coli conjugative ssDNA that is transferred from donor to recipient cells. Using the environmentally relevant redox agents, potassium bromate and hydrogen peroxide, we show that the F episome is remarkably sensitive to weak mutagens during conjugation, enabling the detection of significant differences in mutational spectra induced by these agents. We support our findings with metabolomic analysis, which reveals agent-specific responses in E. coli . We compare these results with those obtained using a yeast ssDNA reporter and conclude that redox-induced mutagenesis depends, among other factors, on the metabolic context of the analysed system. These findings have important implications because the high sensitivity of conjugation-associated ssDNA to environmental mutagens may contribute to the evolution of antibiotic resistance. GRAPHICAL