Terminalia ferdinandiana Fruit and Leaf Extracts Inhibit Methicillin-Resistant Staphylococcus aureus Growth

The development of multiple antibiotic-resistant bacteria has vastly depleted our repertoire of effective antibiotic chemotherapies. The development of multi- beta -lactam-resistant strains are particularly concerning due to our previous reliance on this class of antibiotics because of their initial efficacy and broad-spectrum activity. With increases in extended-spectrum beta -lactam-resistance and an expanded resistance to other classes of antibiotics, there is an urgent need for the development of effective new antibiotic therapies. Terminalia ferdinandiana is an endemic Australian plant known for its high antioxidant and tannin contents. T. ferdinandiana fruit and leaf extracts have strong antibacterial activity against a wide variety of bacterial pathogens. However, T. ferdinandiana extracts have not been tested against ESBL and MRSA antibiotic-resistant pathogens. An objective of this study was to screen T. ferdinandiana fruit and leaf extracts for bacterial growth inhibitory activity by disc diffusion assay against beta -lactam-sensitive and -resistant E. coli strains and against methicillin-sensitive and -resistant S. aureus . The minimum inhibitory concentration (MIC) was quantified by liquid dilution techniques. The fruit methanolic extract, as well as the methanolic, aqueous, and ethyl acetate leaf extracts strongly inhibited the growth of the MRSA, with MICs as low as 223 mu g/mL. In contrast, the extracts were ineffective inhibitors of ESBL growth. Metabolomic fingerprint analysis identified a diversity and relative abundance of tannins, flavonoids, and terpenoids, several of which have been reported to inhibit MRSA growth in isolation. All extracts were nontoxic in the Artemia nauplii and HDF toxicity assays, further indicating their potential for medicinal use.