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Published on: October 13, 2010
A hydrophilic polyimidazolium antibiotic targeting the membranes of Gram-negative bacteria
Yahua Chen1, Melvin Yong1, Ming Li1
1Infectious Diseases Translational Research Programme, Department of Biochemistry, National University of Singapore, Singapore, Singapore.
Objectives:
The rise of MDR Gram-negative bacteria (GNB), especially those resistant to last-resort drugs such as carbapenems and colistin, is a global health risk and calls for increased efforts to discover new antimicrobial compounds. We previously reported that polyimidazolium (PIM) compounds exhibited significant antimicrobial activity and minimal mammalian cytotoxicity. However, their mechanism of action is relatively unknown. We examined the efficacy and mechanism of action of a hydrophilic PIM (PIM5) against colistin- and meropenem-resistant clinical isolates.
Methods:
MIC and time-kill testing was performed for drug-resistant Escherichia coli and Klebsiella pneumoniae clinical isolates. N-phenyl-1-naphthylamine and propidium iodide dyes were employed to determine membrane permeabilization. Spontaneous resistant mutants and single deletion mutants were generated to understand potential resistance mechanisms to the drug.
Results:
PIM5 had the same effectiveness against colistin- and meropenem-resistant strains as susceptible strains of GNB. PIM5 exhibited a rapid bactericidal effect independent of bacterial growth phase and was especially effective in water. The polymer disrupts both the outer and cytoplasmic membranes. PIM5 binds and intercalates into bacterial genomic DNA upon entry of cells. GNB do not develop high resistance to PIM5. However, the susceptibility and uptake of the polymer is moderately affected by mutations in the two-component histidine kinase sensor BaeS. PIM5 has negligible cytotoxicity on human cells at bacterial-killing concentrations, comparable to the commercial antibiotics polymyxin B and colistin.
Conclusions:
PIM5 is a potent broad-spectrum antibiotic targeting GNB resistant to last-resort antibiotics.
Insights
Polyimidazolium (PIM5) effectively targets multidrug-resistant Gram-negative bacteria (GNB), including strains resistant to last-resort antibiotics. This novel compound rapidly kills bacteria by disrupting membranes and DNA, with minimal human cell toxicity.
Area of Science:
- Microbiology
- Infectious Diseases
- Drug Discovery
Background:
- Multidrug-resistant Gram-negative bacteria (GNB) pose a significant global health threat, necessitating the development of novel antimicrobial agents.
- Polyimidazolium (PIM) compounds have demonstrated antimicrobial activity and low cytotoxicity, but their mechanism of action requires elucidation.
- The emergence of resistance to carbapenems and colistin in GNB highlights the urgent need for alternative therapeutic strategies.
Purpose of the Study:
- To investigate the efficacy of a hydrophilic polyimidazolium compound, PIM5, against clinical isolates of colistin- and meropenem-resistant Gram-negative bacteria.
- To elucidate the mechanism of action of PIM5, including its effects on bacterial membranes and DNA.
- To assess the potential for resistance development to PIM5 and its cytotoxicity to human cells.
Main Methods:
- Minimum inhibitory concentration (MIC) and time-kill assays were conducted on drug-resistant Escherichia coli and Klebsiella pneumoniae clinical isolates.
- Membrane permeabilization was assessed using N-phenyl-1-naphthylamine and propidium iodide dyes.
- Spontaneous and single deletion mutants were generated to investigate resistance mechanisms, with a focus on the BaeS two-component system.
Main Results:
- PIM5 demonstrated potent activity against both susceptible and resistant GNB strains, including those resistant to colistin and meropenem.
- The compound exhibited rapid, growth-phase-independent bactericidal effects, particularly in aqueous environments, by disrupting both outer and cytoplasmic bacterial membranes.
- PIM5 was found to bind and intercalate into bacterial genomic DNA post-cellular entry, and high-level resistance did not readily develop. Mutations in BaeS moderately affected susceptibility and uptake.
- Negligible cytotoxicity was observed in human cells at bactericidal concentrations, comparable to polymyxin B and colistin.
Conclusions:
- PIM5 is a highly effective broad-spectrum antibiotic candidate against multidrug-resistant Gram-negative bacteria.
- Its mechanism involves dual membrane disruption and DNA intercalation, offering a promising alternative to last-resort antibiotics.
- PIM5 exhibits a favorable safety profile with low mammalian cell toxicity.
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