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Synthesis and antimicrobial evaluation of a pyrazoline-pyridine silver(I) complex: DNA-interaction and anti-biofilm activity

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Abstract

The emergence of resistant bacterial strains mainly due to misuse of antibiotics has seriously affected our ability to treat bacterial illness, and the development of new classes of potent antimicrobial agents is desperately needed. In this study, we report the efficient synthesis of a new pyrazoline-pyridine containing ligand L1 which acts as an NN-donor for the formation of a novel silver (I) complex 2. The free ligand did not show antibacterial activity. High potency was exhibited by the complex against three Gram-negative bacteria, namely Escherichia coli, Pseudomonas aeruginosa and Acinetobacter baumanii with the minimum inhibitory concentration (MIC) ranging between 4 and 16 μg/mL (4.2–16.7 μM), and excellent activity against the fungi Candida albicans and Cryptococcus neoformans (MIC ≤ 0.25 μg/mL = 0.26 μM). Moreover, no hemolytic activity within the tested concentration range was observed. In addition to the planktonic growth inhibition, the biofilm formation of both Methicillin-resistant Staphylococcus aureus (MRSA) and Pseudomonas aeruginosa was significantly reduced by the complex at MIC concentrations in a dose-dependent manner for Pseudomonas aeruginosa, whereas a biphasic response was obtained for MRSA showing that the sub-MIC doses enhanced biofilm formation before its reduction at higher concentration. Finally, complex 2 exhibited strong DNA binding with a large drop in DNA viscosity indicating the absence of classical intercalation and suggesting the participation of the silver ion in DNA binding which may be related to its antibacterial activity. Taken together, the current results reveal that the pyrazoline-pyridine silver complexes are of high interest as novel antibacterial agents, justifying further in vitro and in vivo investigation.

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Acknowledgements

Antimicrobial and mammalian cell toxicity screening was performed by CO-ADD (The Community for Open Antimicrobial Drug Discovery) (Blaskovich 2015), funded by the Welcome Trust (UK) and The University of Queensland (Australia). The calculations were performed on a computer in the Laboratory of Computer and Analytical Techniques, University of Lodz (Poland). DM and BM were supported by a scholarship co-financed by Greece and the European Union (European Social Fund- ESF) through the Operational Programme «Human Resources Development, Education and Lifelong Learning» in the context of the project “Reinforcement of Postdoctoral Researchers—2nd Cycle” (MIS-5033021), implemented by the State Scholarships Foundation (ΙΚΥ).

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Correspondence to Marina Sagnou.

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Matiadis, D., Karagiaouri, M., Mavroidi, B. et al. Synthesis and antimicrobial evaluation of a pyrazoline-pyridine silver(I) complex: DNA-interaction and anti-biofilm activity. Biometals 34, 67–85 (2021). https://doi.org/10.1007/s10534-020-00263-z

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  • DOI: https://doi.org/10.1007/s10534-020-00263-z

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