INTRODUCTION: Antimicrobial resistance has become a serious threat to humanity, factors such as the inappropriate and excessive use of antibiotics have caused the emergence of resistant strains to available antimicrobial therapies (WHO, 2021). As a result, there is an increase in cases of resistant infections, making treatment difficult or impossible, leading to serious infections and even death (OLIVEIRA et al., 2022). Escherichia coli is a common bacterium that is part of the human microbiota, but there are strains that are pathogenic and multiresistant (KJELSTRUP et al., 2017; QIU et al., 2019). This scenario requires the search for new alternatives to solve or reduce this problem (XU et al., 2019). AIM: Therefore, the objective of this work was to verify the antibacterial activity of 13 2-aminothiophene derivatives and their possible synergies when combined with conventional antibiotics (ampicillin and gentamicin), against standard and multiresistant strains of Escherichia coli. METHODS: The chemical compounds were obtained through the Gewald reaction. A series of 13 compounds derived from 2-aminothiophenes (2-AT) were tested, coded by the following abbreviations and numbers: 1 – 6EST; 2 – 7EST; 3 – 5EST; 4 – 6CN; 5 – 7CN; 6 – 8CN; 7 – 6CNSe; 8 – 7CNSe; 9 – 6-ME-EST; 10 – 6AMD; 11 – 6CN-ME; 12 – 6CN-ET; 13 – 6CN-tBut. A standard strain (Escherichia coli ATCC) and a multi-resistant strain (Escherichia coli 06) were used. To evaluate the Minimum Inhibitory Concentration (MIC), the microdilution method in a 96-well plate was used. To this end, a solution was prepared containing 100 ?L of bacterial inoculum and 900 ?L of liquid culture medium (BHI 10%), of which 100 ?L was distributed into each well. Subsequently, 100 ?L of the test compound was added to the first well, followed by serial microdilution until the penultimate well, the last one being the growth control. Concentrations vary between 1024 and 0.5 ?g/mL (OLIVEIRA-TINTINO et al., 2020). The synergistic activity of the association of 2-AT derivatives and traditional antibiotics was carried out according to Coutinho et al., (2008), in which the compound is tested at subinhibitory concentration (MIC/8). In this way, a solution was prepared, containing 1162 ?L of 10% BHI broth and 150 ?L of the inoculum of each strain and 188 ?L of the compound. Distribution on plates and microdilution of antibiotics (ampicillin and gentamicin) were carried out according to the previous test. All tests were performed in triplicate. RESULTS AND DISCUSSION: No isolated compound showed inhibitory activity as the minimum inhibitory concentration (MIC) was ? 1024 ?g/mL for the 13 compounds against both the standard strain and the multidrug-resistant strain. However, some compounds showed a synergistic effect combined with antibiotics. When tested in combination with ampicillin, only compound 12 was able to reduce the MIC, which for ampicillin was ? 1000 ?g/mL and in combination was reduced to 250?g/mL. When combined with gentamicin (MIC ? 500 ?g/mL), all 13 compounds reduced the MIC, but compounds 3 (5 ?g/mL), 6 (6 ?g/mL), 7 (7 ?g/mL), 9 (3 ?g/mL), 10 (4 ?g/mL), 11 (3 ?g/mL) and 12 (2 ?g/mL) showed better inhibition results, demonstrating better synergism. The combination of biologically active heterocycle rings with antibiotics generally produces a synergistic effect, providing promising results in medicinal chemistry (BOZOROV et al., 2017). A 2-AT compound investigated by Nasr et al., (2014), demonstrated more potent inhibitory activity against E. coli than Gentamicin, activity attributed to the introduction of an adamantyl fragment. A series of compounds with 2-AT and gallic acid moieties were inactive against E. coli, however, they were active against other species of bacteria (MAHDAVI et al., 2020). In E. coli, the mechanism of action involved in resistance to ?-lactams such as ampicillin is linked to a genetic mutation that causes a decrease in the permeability of the cell membrane, being one of the reasons for the increase in resistance (LI et al., 2019). As for aminoglycosides, resistance may be associated with the intergenetic transfer of plasmids that encode resistance (JOHNSON et al., 1994). CONCLUSION: The 2-aminothiophene derivative compounds tested stand out for their synergistic effect and may have interfered with the resistance mechanisms involved, facilitating the action of antibiotics, demonstrating themselves as possible antibiotic adjuvants. Therefore, it is necessary to continue studies to better elucidate the mechanisms of action involved.
ACKNOWLEDGMENT
We thank the Federal University of Paraíba (UFPB), State University of Paraíba (UEPB) and Regional University of Cariri (URCA) for their partnership in carrying out the trials. To the Coordination for the Improvement of Higher Education Personnel (CAPES) for financing the scholarship (Process: 88887.7213/2022-00).
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Comissão Organizadora
Francisco Mendonça Junior
Pascal Marchand
Teresinha Gonçalves da Silva
Isabelle Orliac-Garnier
Gerd Bruno da Rocha
Comissão Científica
Ricardo Olimpio de Moura
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