Avaliação da atividade antibacteriana e sinergismo do óleo essencial obtido das folhas de croton conduplicatus com cefalosporinas frente a cepas clínicas de MRSA

Abstract

This study aimed to investigate the antimicrobial activity of the essential oil from Croton conduplicatus leaves (OECC) against Staphylococcus aureus strains, including methicillinresistant variants (MRSA), as well as to evaluate the interaction of OECC with cephalosporinclass antibiotics and its cytotoxicity on erythrocytes. For this purpose, the leaves were collected, dried, and ground, and the essential oil was extracted by hydrodistillation. The chemical composition of OECC was analyzed by gas chromatography coupled to mass spectrometry (GC-MS). Six S. aureus strains were tested to determine the minimum inhibitory concentration (MIC) and minimum bactericidal concentration (MBC) of OECC and antibiotics (cefepime, ceftazidime, and ceftriaxone) using the broth microdilution method. The interaction between OECC and antibiotics was evaluated by the checkerboard assay, calculating the fractional inhibitory concentration index (FICI). MIC determinations followed CLSI guidelines (2017), with concentrations ranging from 2,048 to 4 µg/mL for antibiotics and from 1,024 to 512 µg/mL for OECC. MBC was established by subculturing on Mueller-Hinton agar from wells without visible growth. The checkerboard assay determined FICI values where ≤ 0.5 indicated synergy, between 0.5 and 4 indicated indifference, and > 4 suggested antagonism, according to Lorian’s classification (2005). Cytotoxicity was evaluated by measuring hemolysis in sheep erythrocytes via spectrophotometry. Results showed that OECC exhibits antimicrobial activity against S. aureus and MRSA, demonstrating synergy when combined with cephalosporins, which allows for reduced antibiotic concentrations. Additionally, the oil showed low cytotoxicity in erythrocytes, suggesting its potential use as an adjuvant agent in treating resistant bacterial infections. This study contributes to the understanding of how essential oils can be used in treating bacterial infections, especially those caused by resistant strains. The combination of essential oils with antibiotics may be an effective strategy to reduce bacterial resistance and improve therapeutic outcomes, but further research is necessary to optimize clinical use of this approach.