Chemical Profile with Antibacterial and Modulatory Activity of Extracts from the Stem Bark of Cnidoscolus quercifolius Pohl.

Objective: The present study aimed to investigate the chemical profile and evaluate the antibacterial and antibiotic-modulating activity of the methanolic extract and ethyl acetate of the stem bark of C. quercifolius against standard and multiresistant strains. Methods: The Minimum Inhibitory Concentration was determined by the microdilution method, and the modulating potential of the extracts on aminoglycoside and β-lactam antibiotics was evaluated. Results: The classes of secondary metabolites identified from qualitative chemical prospecting were flavones, flavonols, xanthones, flavonones, flavonols, catechins and leucoanthocyanidins. The assays showed inhibition only for Klebsiella pneumoniae-producing extended-spectrum β- lactamase, Klebsiella pneumoniae carbapenemase and Escherichia coli ATCC 25922 with MICs of 256, 512 and 512 μg/mL, respectively. The extracts, when associated with gentamicin and amoxicillin, showed synergism against all standard and multiresistant strains, with the exception of Klebsiella pneumoniae carbapenemase and Klebsiella pneumoniae producing extendedspectrum β-lactamase, respectively. When combined with amikacin, they also demonstrated synergism against multidrug-resistant strains; however, only the ethyl acetate extract had a synergistic effect against E. coli ATCC 25922. The association of penicillin with methanolic extract showed synergism only for Klebsiella pneumoniae producing extended-spectrum β-lactamase and S. aureus ATCC 29213, while the ethyl acetate extracts demonstrated synergism against S. aureus and Klebsiella pneumoniae producing extended-spectrum β-lactamase. Conclusion: It was found that C. quercifolius extracts have antibacterial potential against gramnegative bacteria. However, the need for additional research using specific methods against bacteria carrying different resistance mechanisms, especially gram-positive ones, is highlighted, with the aim of elucidating their mechanism of action. conclusion: The species was found to have substances with potential against Gram-negative bacteria. However, the need for additional research using specific methods against bacteria carrying different resistance mechanisms, especially Gram-positive ones, is highlighted, with the aim of elucidating their mechanism of action.