Complexos de Paládio(II) e Platina(II) ligados a β-dicetonas como estratégia de controle Campylobacter jejuni na indústria avícola

Abstract

Campylobacter jejuni is the main etiological agent responsible for bacterial gastroenteritis worldwide. Campylobacteriosis is frequently associated with the consumption of contaminated foods, especially chicken meat. Factors such as the ability to colonize different environments, form biofilms, and exhibit increasing resistance to antibiotics represent a major challenge for controlling this pathogen in the food production chain and for public health. In this context, the search for new antimicrobial agents has intensified, with particular emphasis on metal-based compounds with potential biological activity. Metal complexes containing β-diketone ligands have attracted interest due to their structural stability, chemical versatility, and potential to interact with biological systems. This thesis was structured into three chapters. The first chapter is dedicated to general considerations and the theoretical background of the topics addressed in the subsequent chapters. The second chapter aimed to evaluate the efficacy of palladium metal complexes bound to β-diketonates and dimethyl sulfoxide (DMSO), with the formulas [Pd²⁺Cl₂(4,4,4-trifluoro-1-(2-thienyl)-1,3-butanedione)(DMSO)] (PdDMSOTTA) and [Pd²⁺Cl₂(4,4,4-trifluoro-1-phenyl-1,3-butanedione)(DMSO)] (PdDMSOBTA). The third chapter aimed to investigate the activity of platinum complexes bound to β-diketones, with the formulas [Pt²⁺Cl₂(4,4,4-trifluoro-1-(2-thienyl)-1,3-butanedione)(DMSO)] (PtDMSOTTA) and [Pt²⁺Cl₂(4,4,4-trifluoro-1-phenyl-1,3-butanedione)(DMSO)] (PtDMSOBTA). The tests were conducted on six C. jejuni strains resistant to erythromycin and ciprofloxacin, evaluated in both planktonic and sessile forms. The bactericidal activity of the complexes was determined through the minimum bactericidal concentration (MBC). All strains were classified according to the biofilm formation index (BFI) as non-producers, weak, moderate, or strong biofilm producers, while antibiofilm activity was evaluated through mature biofilm eradication assays. The ultrastructure of the biofilms was analyzed by scanning electron microscopy, the metabolomic profile by gas chromatography coupled with mass spectrometry (GC–MS), and cytotoxicity in differentiated Caco-2 cells by the resazurin reduction assay. The tests presented in Chapter Two show the results for palladium complexes coordinated to β-diketones. The PdDMSOBTA complex exhibited greater bactericidal activity against planktonic cells, with an average MBC of 15.36 µg/mL, eliminating all strains at concentrations < 50 µg/mL, whereas PdDMSOTTA showed lower efficacy. In biofilms, PdDMSOBTA promoted complete elimination at concentrations < 400 µg/mL and significantly reduced the adhered biomass, with an average reduction of approximately 75% in the biofilm formation index. Metabolomic analysis revealed alterations in metabolic pathways related to amino acid metabolism, purine metabolism, and cellular stress response. The viability of Caco-2 cells remained above 80–90% after exposure to the compounds, indicating low cytotoxicity. In Chapter Three, the antimicrobial potential of platinum(II) β-diketonate complexes, PtDMSOBTA and PtDMSOTTA, was investigated against the same six resistant strains of C. jejuni. The PtDMSOBTA complex showed higher bactericidal activity in the planktonic form, with an average MBC of 12.76 µg/mL, while PtDMSOTTA showed lower efficacy. In biofilms, PtDMSOBTA eliminated all isolates at concentrations < 200 µg/mL and significantly reduced biofilm biomass, whereas PtDMSOTTA showed a moderate effect. Scanning electron microscopy revealed structural disorganization of the biofilms and reduction of the extracellular matrix. Metabolomic analysis identified alterations in pathways related to amino acid metabolism, redox balance, and tryptophan metabolism. Both complexes showed low cytotoxicity, with cell viability between 80 and 100%. The study allowed the conclusion that palladium(II) and platinum(II) β-diketonate complexes, especially PdDMSOBTA and PtDMSOBTA, containing the ligand 4,4,4-trifluoro-1-phenyl-1,3-butanedione, exhibit significant antimicrobial activity against C. jejuni in both planktonic and sessile forms. planktonic cells, concentrations up to 100 µg/mL were sufficient to eliminate the microorganism, possibly due to metabolic alterations associated with the induction of cellular stress. In addition, the compounds showed low cytotoxicity in eukaryotic cells, indicating an initial profile of biological safety. Regarding the sessile form, higher concentrations were required for biofilm eradication, and additional cytotoxicity studies are still necessary to confirm safety under these conditions. Overall, the results obtained highlight the potential of these metal complexes as promising alternatives for the control of C. jejuni, especially in strategies aimed at reducing contamination in environments related to food production and processing.