Aims: Polymyxins are an important last-line treatment for infections caused by multidrug-resistant Gram-negative bacteria. Nonetheless, the emergence of polymyxin-resistance and the limiting of polymyxin monotherapy urgently demands its optimisation. Aquilaria malaccensis (Agarwood) has been widely used as traditional medicine. Many parts of the plant including leaves exhibit a considerable in vitro antibacterial activity against microbial pathogens. Exploiting A. malaccensis in combination with polymyxins provides a novel strategy in fighting antimicrobial resistance. The objective of this study was to evaluate the combination effects of A. malaccensis extract with polymyxins against Acinetobacter baumannii and Klebsiella pneumoniae. Methodology and results: In vitro time-kill studies and GC-MS analysis were performed to evaluate the bacterial killing of polymyxin B and extract combination and analyse chemical compounds of the extract, respectively. The combination of polymyxin B (1 mg/L) and A. malaccensis extract (32 mg/mL and 64 mg/mL) treatments exhibited enhanced bacterial killing compared to polymyxin B alone at 4 h and 24 h. Combination treatments also inhibited the bacterial growth of both A. baumannii and K. pneumoniae observed throughout the 24 h. More than sixty compounds including phytol, 9,12-octadecadienal, fatty acid, alkanes and terpenoids were putatively identified as the compounds that likely contributed to the antibacterial activity. Conclusion, significance and impact of study This study was the first to report the potential application of A. malaccensis extract in combination with polymyxin B in treatment against A. baumannii and K. pneumoniae and can be further investigated and optimized for the treatment of bacterial infectious diseases.
Thymelaeaceae ; Polymyxins ; Acinetobacter baumannii--immunology ; Klebsiella pneumoniae--immunology

Aims: The exploration of natural products with innovative uses is dynamic and expanding rapidly. Medicinal plants have fascinated many researchers that subsequently lead to research publications highlighting plant extracts with wide range of secondary metabolites such as flavonoids, alkaloids, glycosides, quinones, terpenoids, tannins and saponins that exhibit antimicrobial activities and disease control. The concentration of these bioactive compounds in each plant species varies based on the pathosystem and environmental conditions. This study aims to uncover the various types of phytochemicals with antifungal properties. Methodology and results: Seven categories of plant-based antifungal compounds were reviewed, which are terpenoids, saponins, phenolic compounds, coumarins, alkaloids, essential oils and peptides, with examples and structures of some available compounds. The mechanism of action of each category of phytochemical was discussed. Also, the impact of some compounds was explained and elaborated. Conclusion, significance and impact of study It is of a great importance to explore natural plant fighters against fungal infection. Those active plant components do not only have antifungal properties, but they also help in the healing process and some even exhibit anticancer activities. The development and knowledge of antifungal activities from plant extracts have the potential for applications in antifungal therapy. Since the exact description of how antifungal compounds function in the human body is still unclear more studies are required to unveil phytochemicals’ properties and to elucidate their effects on living cells.
Phytochemicals--therapeutic use ; Antifungal Agents