نبذة مختصرة : Staphylococcus aureus is an opportunistic pathogen, which can cause since skin to disseminated infections. The increase in antimicrobial resistance (AMR) is linked to the emergence of S. aureus strains resistant to one or multiple antibacterial classes. Searching for new compounds with antibacterial activity is growing. Combretum genus comprises tropical plants, whose use is reported in folk medicine due to anti inflammatory, antiparasitic and antimicrobial properties. Therefore, this work aimed to evaluate if extracts of three native Combretum species are active against S. aureus. Six S. aureus strains were used, where three expresses efflux pumps. Ethanolic and aqueous extracts from the leaves of Combretum duarteanum, Combretum mellifluum and Combretum leprosum were used. Initially, the resistance profile was characterized by antibiograms and detection of aminoglycoside resistance genes by polymerase chain reaction (PCR) method. An initial screening of the extracts was performed at 0.5 mg/mL, followed by bioassays for Minimum Inhibitory Concentration (MIC) and Minimum Bactericidal Concentration (MBC) determination. Antibiotic-extract modulation tests were also performed by combining norfloxacin or streptomycin with C. duarteanum ethanolic extract (CDEN). The assays were performed on independent triplicates, analyzed by spectrophotometry and resazurin. Strains showed more resistance to amikacin, gentamicin and penicillin G. C. duarteanum and C. mellifluum extracts showed antibacterial activity at 0.5 mg/mL in the screening. MIC values ranged from 0.062 to 0.5 mg/mL; ethyl acetate fraction of C. duarteanum (CDEN AcOEt) showed bactericidal activity against most strains. CDEN extract showed modulation factor (MF) when combined with norfloxacin (2 to 4) and streptomycin (8 to 32), and CDEN-AcOEt fraction had a synergistic action with streptomycin (FICI = 0.039) against S. aureus ATCC 912415. Thus, it is concluded that C. duarteanum and C. mellifluum species are promising sources of new anti-S. aureus ...
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