Combating Enteroaggregative <i>Escherichia coli:</i> Dual antibacterial and antibiofilm effects of silver- and copper-1,10-phenanthroline-5,6-dione complexes

Caroline Gastaldi Guerrieri; Mariane Vedovatti Monfardini Sagrillo; Solange Alves Vinhas; Michael Devereux; Malachy McCann; Thaís Pereira de Mello; Liliana Cruz Spano; André Luis Souza dos Santos; Caroline Gastaldi Guerrieri; Mariane Vedovatti Monfardini Sagrillo; Solange Alves Vinhas; Michael Devereux; Malachy McCann; Thaís Pereira de Mello; Liliana Cruz Spano; André Luis Souza dos Santos

doi:10.3934/microbiol.2025036

AIMS Microbiology

2025, Volume 11, Issue 4: 855-876. doi: 10.3934/microbiol.2025036

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Research article

Combating Enteroaggregative Escherichia coli: Dual antibacterial and antibiofilm effects of silver- and copper-1,10-phenanthroline-5,6-dione complexes

Caroline Gastaldi Guerrieri ¹,
Mariane Vedovatti Monfardini Sagrillo ¹,
Solange Alves Vinhas ²,
Michael Devereux ³,
Malachy McCann ⁴,
Thaís Pereira de Mello ⁵,
Liliana Cruz Spano ¹,
André Luis Souza dos Santos ^{5
,
,}

1.
Department of Pathology, Health Sciences Center, Federal University of Espírito Santo, Vitória, Espírito Santo, Brazil
2.
Núcleo de Doenças Infecciosas, Health Sciences Center, Federal University of Espírito Santo, Vitória, Espírito Santo, Brazil
3.
Centre for Biomimetic and Therapeutic Research, Focas Research Institute, Technological University Dublin, Dublin, Ireland
4.
Chemistry Department, Maynooth University, Maynooth, Ireland
5.
General Microbiology Department, Institute of Microbiology Paulo de Góes, Federal University of Rio de Janeiro, Rio de Janeiro, Brazil

Received: 19 September 2025 Revised: 06 November 2025 Accepted: 13 November 2025 Published: 18 November 2025

Enteroaggregative Escherichia coli (EAEC) causes acute and persistent diarrhea. Its antimicrobial resistance and strong biofilm formation hinder treatment, highlighting the need for new therapies. This study evaluated the antimicrobial efficacy of 1,10-phenanthroline-5,6-dione (phendione) and its copper [Cu(phendione)₃](ClO₄)₂.4H₂O (Cu-phendione) and silver [Ag(phendione)₂]ClO₄ (Ag-phendione) complexes against planktonic and biofilm-forming EAEC cells. The minimum inhibitory concentration (MIC) and minimum bactericidal concentration (MBC) values were determined for planktonic cells of 35 clinical EAEC isolates, revealing potent antibacterial activity by all test compounds, with Cu-phendione showing the greatest efficacy, followed by Ag-phendione and phendione. Most combinations of Cu-phendione or Ag-phendione with either ampicillin or tetracycline exhibited additive effects through checkerboard assays, whereas time-kill experiments revealed synergistic interactions between the complexes and those classical antibacterial agents. Minimum biofilm inhibitory concentration (MBIC) analysis identified Cu-phendione as the most effective compound for disarticulating biofilm formation (geometric MBIC = 14.61 µM), followed by Ag-phendione (24.69 µM) and phendione (67.08 µM). Notably, Cu-phendione eradicated biofilms in 24 isolates (68.6%), while Ag-phendione and phendione achieved eradication in 11 (31.4%) and 6 (17.1%) isolates, respectively. Furthermore, the test complexes were able to disrupt established mature biofilms, as demonstrated by the crystal violet assay and scanning electron microscopy. In combination therapy, complete biofilm eradication was achieved in all clinical isolates tested when Cu-phendione was paired with cefoxitin, tobramycin, tetracycline, or ciprofloxacin. Collectively, phendione-derived complexes, particularly Cu-phendione, represent promising candidates for the treatment of EAEC infections in planktonic and biofilm-associated states.
- EAEC,
- diarrhea,
- antimicrobial resistance,
- biofilm,
- coordination compounds,
- copper complex
Citation: Caroline Gastaldi Guerrieri, Mariane Vedovatti Monfardini Sagrillo, Solange Alves Vinhas, Michael Devereux, Malachy McCann, Thaís Pereira de Mello, Liliana Cruz Spano, André Luis Souza dos Santos. Combating Enteroaggregative Escherichia coli: Dual antibacterial and antibiofilm effects of silver- and copper-1,10-phenanthroline-5,6-dione complexes[J]. AIMS Microbiology, 2025, 11(4): 855-876. doi: 10.3934/microbiol.2025036

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Abstract

Enteroaggregative Escherichia coli (EAEC) causes acute and persistent diarrhea. Its antimicrobial resistance and strong biofilm formation hinder treatment, highlighting the need for new therapies. This study evaluated the antimicrobial efficacy of 1,10-phenanthroline-5,6-dione (phendione) and its copper [Cu(phendione)₃](ClO₄)₂.4H₂O (Cu-phendione) and silver [Ag(phendione)₂]ClO₄ (Ag-phendione) complexes against planktonic and biofilm-forming EAEC cells. The minimum inhibitory concentration (MIC) and minimum bactericidal concentration (MBC) values were determined for planktonic cells of 35 clinical EAEC isolates, revealing potent antibacterial activity by all test compounds, with Cu-phendione showing the greatest efficacy, followed by Ag-phendione and phendione. Most combinations of Cu-phendione or Ag-phendione with either ampicillin or tetracycline exhibited additive effects through checkerboard assays, whereas time-kill experiments revealed synergistic interactions between the complexes and those classical antibacterial agents. Minimum biofilm inhibitory concentration (MBIC) analysis identified Cu-phendione as the most effective compound for disarticulating biofilm formation (geometric MBIC = 14.61 µM), followed by Ag-phendione (24.69 µM) and phendione (67.08 µM). Notably, Cu-phendione eradicated biofilms in 24 isolates (68.6%), while Ag-phendione and phendione achieved eradication in 11 (31.4%) and 6 (17.1%) isolates, respectively. Furthermore, the test complexes were able to disrupt established mature biofilms, as demonstrated by the crystal violet assay and scanning electron microscopy. In combination therapy, complete biofilm eradication was achieved in all clinical isolates tested when Cu-phendione was paired with cefoxitin, tobramycin, tetracycline, or ciprofloxacin. Collectively, phendione-derived complexes, particularly Cu-phendione, represent promising candidates for the treatment of EAEC infections in planktonic and biofilm-associated states.

Acknowledgments

We thank Dr. Isabel C. A. Scalestky for kindly providing the EAEC 042 reference strain, and the Laboratório de Ultraestrutura Celular Carlos Alberto Redins (LUCCAR)-UFES (MCT/FINEP/CT-INFRA – PROINFRA 01/2006) for the Scanning Electron Microscopy analysis.
This study was supported by the Brazilian agencies: CNPq (Conselho Nacional de Desenvolvimento Científico e Tecnológico), CAPES (Coordenação de Aperfeiçoamento de Pessoal de Nível Superior, Financial code 001), FAPES (Fundação de Amparo à Pesquisa e Inovação do Espírito Santo) and FAPERJ (Fundação de Amparo à Pesquisa do Estado do Rio de Janeiro).

Conflict of interest

The authors declare no conflict of interest.

Author contributions

C.G.G. conducted the experiments and wrote the manuscript. M.V.M.S. and S.A.V. conducted the experiments. M.D. and M.M. synthesized the compounds. T.P.M. wrote the manuscript. L.C.S and A.L.S.S. designed, supervised the study and wrote the manuscript. All authors reviewed and approved the final version of the manuscript.

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