Antibacterial Activity of Crude Extract and Fractions from Melaleuca leucadendra (L.) L. Flowers

The emergence of clinically available antibiotic-resistant strains has been reported with worrisome regularity over the past 20 years. This increasing evolution of bacterial resistance, associated with the present scarce therapeutic arsenal, has led to the appearance of severe and persistent infections. About 75% of the antimicrobial compounds approved in the last three decades have natural origin which justifies the search for new antimicrobial agents from plant extracts. Several studies have demonstrated the pharmacological potential of the essential oil and some extracts of Melaleuca leucadendra (L.) L. (Myrtaceae) leaves, including antibacterial and antifungal activities. Terpene and flavonoid compounds are the main secondary metabolites related to the antimicrobial activity of M. leucadendra leaves, while the chemical composition of the flowers has been studied by our research group. Thus, this work aimed to evaluate the antibacterial activity of crude ethanolic extract (CEE) and fractions obtained from M. leucadendra flowers. The CEE was obtained by exhaustive maceration and fractions from successive liquid-liquid partitions with increasing polarity solvents: n-hexane, dichloromethane, ethyl acetate, n-butanol and methanol/water to get the fractions. Antimicrobial activity screening was performed using agar well diffusion assay. For microorganisms considered susceptible (zone of inhibition with a size diameter equal to or greater than 10 mm), the minimum inhibitory concentration (MIC) assay was performed by broth microdilution method. The growth of all evaluated microorganisms was inhibited for at least one sample, except for P. mirabilis and K. pneumoniae. Tested samples and antibiotic MIC values are presented in Table 1. The CEE and fractions did not demonstrate activity against Gram-negative bacteria which are known to have greater antibiotic resistance. For Gram-positive bacteria, the CEE was more promising because it presented MIC below 2.5 mg/mL for all species tested. This can be explained by synergistic or additive effects from secondary metabolites present in the CEE which were relatively partitioned in the others organic fractions. In conclusion, the CEE of M. leucadendra flowers presented antibacterial potential against Gram-positive species of clinical importance.
Financial support: UFOP, CAPES, FAPEMIG.