Antimicrobial activity of Backhousia citriodora (lemon myrtle) methanolic extracts

Abstract

Introduction: Backhousia citriodora is a native Australian plant with uses as a bush food component as well as in toiletries and cosmetics. Essential oils produced from leaves of this plant have reputed antiseptic properties. Despite this, solvent extractions of Backhousia citriodora leaves have not been rigorously examined for antiseptic properties. Methods: The antimicrobial activity of methanolic leaf extracts of Backhousia citriodora was investigated by disc diffusion and growth time course assays against a panel of bacteria and fungi. Toxicity was determined using the Artemia franciscana nauplii bioassay. Results: B. citriodora leaf methanolic extract proved to be a versatile antibacterial agent inhibiting the growth of 12 of the 14 bacteria tested (86%). Only C. fruendii and S. aureus growth were unaffected by B. citriodora extract. Gram-positive and Gram-negative bacteria were both affected by B. citriodora extract although Gram-negative bacteria appeared more susceptible. The extract also displayed antifungal activity against a nystatin resistant strain of Aspergillus niger but did not affect Candida albicans or Saccharomyces cerevisiae growth. The antibacterial activity of B. citriodora extract was further investigated by growth time course assays which showed significant growth inhibition in cultures of Bacillus cereus, Bacillus subtilis, Aeromonas hydrophilia and Pseudomonas fluorescens within 1 h. The extract displayed low toxicity in the Artemia franciscana nauplii bioassay. Conclusions: The low toxicity of the methanolic extract and its inhibitory bioactivity against a panel of bacteria validate Australian Aboriginal usage of B. citriodora as an antiseptic agent and confirms its medicinal potential.

A Comparison of the Antimicrobial Activity and Toxicity of Six Combretum and Two Terminalia Species from Southern Africa

“…Indeed, good efficacies (generally in the range 200-5000 μg/ml) are reported for all Combretum extracts against both Gram-positive and Gram-negative bacteria. In contrast, previous studies with plant species of other families generally report a greater susceptibility of Gram-positive bacteria towards solvent extracts for South American,[ 25 ] Australian[ 26 27 28 29 30 ] and other African[ 31 ] plant extracts, although examples of plants having a greater effect on Gram-negative bacteria have also been reported. [ 17 18 ]…”

South African food and medicinal plant extracts as potential antimicrobial food agents

“…Edible plants and plant products (extracts and oils) have been used in foods since ancient times as flavouring agents, as well as food preservatives and folk medicines due to their antimicrobial activities. The growth inhibitory properties of many edible plant extracts against panels of bacteria and fungi associated with food spoilage and food poisoning has been well established (Vesoul and Cock 2012;Boyer and Cock 2013;Cock 2012;Cock and Mohanty 2011).…”

An examination of the antibacterial, antifungal, anti-Giardial and anticancer properties of Kigelia africana fruit extracts

“…Results within this laboratory [43,[48][49][50] have also confirmed the greater susceptibility of Gram-positive bacteria towards other plant extracts, although other examples of plants having a greater effect on Gram negative bacteria have also been reported. [27][28][29]51,52] The K. africana fruit extracts were particularly potent inhibitors of P. mirabilis. This activity is noteworthy as P. mirabilis has been implicated in urinary tract infections (UTI's) and the induction of rheumatoid arthritis (RA) [17] .…”