Membrane Potential-Dependent Uptake of Cationic Oligoimidazolium Mediates Bacterial DNA Damage and Death

With the rise of anti-microbial resistance (AMR), there is a need to develop antimicrobials with novel mechanisms of action. Among them, polyimidazolium PIM1 was identified as one of the potent antimicrobial against a wide variety of multi-drug resistant nosocomial pathogens.

Due to the heterogeneity of PIM1, an oligomer of PIM1 with 6 repeating imidazolium subunits, namely OIM1-6 was used for this study. The result showed that OIM1-6 resistance is associated with lower membrane potential & drug uptake.

It was also discovered that OIM1-6 resulted in dsDNA breaks through intracellular binding. Through an in-vitro gel migration assay, it was noted that OIM1-6 slowed down DNA band migration. In addition, OIM1-6 could displace picogreen binding in a concentration-dependent manner. Using E.coli Gam-GFP strain, which is engineered for detecting dsDNA breaks that manifests in the form of GFP foci under microscopy, it was observed in Fig.1 that OIM1-6-treated cells exhibited more foci as compared to untreated cells. DNA damage response genes lexA were also significantly induced upon OIM1-6 treatment.

Taken together, these results showed that OIM1-6 enters the cytoplasm, leading to DNA binding and dsDNA breaks, eventually triggering SOS response.

Fig.1 OIM1-6 treatment leads to double-stranded DNA breaks and the induction of the expression of SOS response genes in E. coli. (A) Representative confocal images of the E. coli MG1655 SMR14334 Gam-GFP strain without any treatment (negative control), treated with 10 mM hydrogen peroxide (positive control), or treated with 1× MIC OIM1-6 for 2 h in MHB at 37°C. The green color represents the Gam-GFP signal, and the blue color represents the DNA dye Hoechst. Foci formation indicates double-stranded DNA breaks, and these are marked by the red arrows in the zoomed-in images.

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¹Yong Loo Lin School of Medicine, National University of Singapore, Singapore. ²School of Chemical Engineering and Biotechnology, Nanyang Technological University, Singapore. ³Centre for Antimicrobial Engineering, Nanyang Technological University, Singapore. ⁴School of Biological Sciences, Nanyang Technological University, Singapore.