An examination of the medicinal potential ofPlanchonella queenslandica: toxicity, antibacterial, and antiviral activities

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Planchonella queenslandica (family Sapotaceae) is an Australian native plant with a history of indigenous Australian medicinal usage. Its antimicrobial activity was investigated by disc diffusion assays against a bacterial panel. Antiviral activity was determined using an MS2 bacteriophage plaque reduction model system. Toxicity was determined using the Artemia franciscana nauplii bioassay. Methanol, water and ethyl acetate leaf extracts displayed antibacterial activity. The methanol and ethyl acetate extracts had the broadest specificity, inhibiting the growth of 9 of the 14 bacteria tested (64 %) respectively. The water extract inhibited the growth of 6 of the 14 bacteria tested (43 %). All extracts were more effective against Gram-positive than Gram-negative bacteria. The methanol and ethyl acetate extracts each inhibited the growth of 100 % of the Gram-positive species tested and 5 of the 9 (56 %) Gram-negative bacteria. The water extract inhibited 3 of the 4 (75 %) Gram-positive bacteria and 3 of the 9 (33 %) of the Gram-negative bacteria tested. The methanol, water and ethyl acetate extracts also displayed antiviral activity in the MS2 plaque reduction assay, inhibiting 90.8 ± 2.4 %, 50.7 ± 5.8 and 71.7 ± 4.4 % of MS2 plaque formation respectively. All extracts were also shown to be non-toxic or of low toxicity in the Artemia fransiscana bioassay. The low toxicity of the P. queenslandica extracts and their inhibitory bioactivity in the MS2 bacteriophage reduction bioassay and against a panel of bacteria validate Australian Aboriginal usage as an antiseptic agent and confirms their medicinal potential.