Antibacterial screening of hexane extracts from Psidium myrtoides, a Brazilian native plant

Even though Brazil has a large biodiversity of medicinal plants, many of them have not had their chemical and biological potential acknowledged. Several medicinal plants are rich in secondary metabolites with broad antibacterial activity, a relevant fact since many pathogenic bacteria are resistant to conventional antibiotics. Psidium myrtoides, a species of plant in the Myrtaceae family that is known for its sweet purple fruit, should be highlighted in this field. It is a medicinal plant with strong antibacterial, antifungal, anti-inflammatory, antioxidant, antitumoral, and herbicidal potential. This study aimed at investigating, for the first time, the antibacterial activity of hexane extracts from P. myrtoides dry leaves – which were collected in both dry and rainy seasons – and the dry pericarp of unripe fruit. Their antibacterial activity was evaluated in vitro by the broth microdilution method on 96-well plates, and their Minimum Inhibitory Concentration (MIC) values were expressed as µg/mL. The following bacteria were assayed: Streptococcus mutans, S. sobrinus, S. mitis, S. salivarius, S. sanguinis, Enterococcus faecalis, Lactobacillus casei, Xanthomonas citri (resistant, tolerant, and sensitive to copper), Mycobacterium tuberculosis, M. avium, and M. kansasii. The resulting MIC values of all extracts under study were promising since they ranged from 31.25 to 500 µg/mL. This study revealed the in vitro potential of P. myrtoides against different bacterial strains and reinforced the need for further phytochemical investigations that aim at isolating its bioactive chemical constituents.