Growth Inhibitory Activity of Kakadu Plum Extracts Against the Opportunistic Pathogenclostridium Perfringens: New Leads in the Prevention and Treatment of Clostridial Myonecrosis

Introduction: Clostridium perfringens is the etiological agent of clostridial myonecrosis and enteritis necroticans. Infections result in exotoxin production, tissue necrosis and unless promptly treated, may result in death. Terminalia ferdinandiana (Kakadu plum) fruit has documented therapeutic properties as a general antiseptic agent. Fruit extracts have been reported to inhibit the growth of an extensive panel of pathogenic bacteria. Leaf extracts have also been shown to block the growth of several bacterial species associated with autoimmune inflammatory diseases. Methods: T. ferdinandiana fruit and leaf solvent extracts were investigated for growth inhibitory activity by disc diffusion assay against a clinical strain of Clostridium perfringens. Their MIC values were determined to quantify and compare their efficacies. Toxicity was determined using the Artemia franciscana nauplii bioassay. Active extracts were analysed by non-targeted HPLC-QTOF mass spectroscopy (with screening against 3 compound databases) for the identification and characterisation of individual components in the crude plant extracts. Results: Methanolic and aqueous T. ferdinandiana fruit and leaf extracts, as well as the leaf ethyl acetate extract, displayed growth inhibitory activity in the disc diffusion assay against C. perfringens. The leaf extracts were generally more potent growth inhibitors than the corresponding fruit extracts, although the aqueous fruit extract had substantially greater efficacy than the aqueous leaf extract. The methanolic and ethyl acetate leaf extracts were particularly potent growth inhibitors, with MIC values of 206 and 117 μg/ml respectively. The fruit methanolic extract also displayed good efficacy, with an MIC of 716 μg/ml. In contrast, the chloroform and hexane extracts of both fruit and leaf were completely devoid of growth inhibitory activity. All T. ferdinandiana extracts were either nontoxic or of low toxicity in the Artemia fransiscana bioassay. Non-biased phytochemical analysis of the methanolic and ethyl acetate leaf extracts revealed the presence of high relative levels of a diversity of galloand ellagi- tannins. Conclusion: The low toxicity of the T. ferdinandiana extracts and the potent growth inhibitory bioactivity of the leaf methanolic and ethyl acetate extracts against C. perfringens indicates their potential as medicinal agents in the treatment and prevention of clostridial myonecrosis and enteritis necroticans. Metabolomic profiling studies indicate that these extracts contained a diversity of tannins.