Antibacterial Activity of Selected Australian Native Plant Extracts

Thirty nine methanolic extracts from twenty five Australian native plants were investigated for their antibacterial activity against two Gram-positive (Bacillus cereus, Bacillus subtilis) and two Gram negative (Aeromonas hydrophilia, Pseudomonas fluorescens) bacterial species using the disc diffusion assay. Twenty eight of the thirty nine extracts tested (72%) inhibited the growth of one or more bacteria. B. cereus was the most susceptible bacteria with twenty one extracts (54%) inhibiting its growth. In comparison, fifteen extracts (38%) inhibited the growth of P. fluorescens, thirteen extracts (33%) inhibited the growth of B. subtilis, and ten extracts (26%) inhibited the growth of A. hydrophilia. Backhousia citriodora and Callistemon citrinus were particularly effective antibacterial agents, being capable of inhibiting the growth of all four bacteria. Acacia aulacocarpa, Buckinghamia celsissima, Callistemon salignus, Allocasuarina littoralis, Eucalyptus major, Leptospermum bracteata, Leptospermum juniperium and Syzygium australe were also good antibacterial agents, each being capable of inhibiting the growth of the majority of bacteria tested.

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