Comparison of visual observation and emission intensity of resazurin for antimicrobial properties of hexane, dichloromethane, methanol and water extracts from a brown alga, Turbinaria ornata

Abstract

Marine natural products have been increasingly found to be a promising source of drug candidates for fighting human diseases. The present study was carried out to assess the antimicrobial properties of a brown alga, Turbinaria ornata. Hexane, dichloromethane, methanol, and water extracts were tested against 23 micro-organisms including Gram-positive and negative bacteria, yeasts, and fungi. The disk diffusion method was employed followed by modified resazurin microtitre assay (REMA). The results obtained from modified REMA using both methods of colorimetric and fluorometric were compared. The best antimicrobial activity was recorded in dichloromethane extract for disk diffusion. Further, modified REMA showed inhibition in Bacillus cereus, Bacillus subtilis, Staphylococcus aureus ATCC 25923, S. aureus, Staphylococcus epidermidis, Staphylococcus saprophyticus, Enterococcus faecalis, Pseudomonas aeruginosa ATCC 27853, Candida parapsilosis ATCC 22019, Candida guilliermondii ATCC 6260, and Saccharomyces cerevisiae. Both methods of modified REMA were substantially in agreement with each other based on Cohen’s kappa statistical analysis (κ value = 0.712; p < 0.0005). Our findings suggested that T. ornata dichloromethane extract has the potential to be used as a source of antimicrobial compounds.

Keywords:

• antibacterial
• antifungal
• antimicrobial
• seaweed
• Turbinaria ornata

Public Interest Statement

Micro-organisms constantly evolve to adapt to new environments. As such, antimicrobial resistance is the ability of micro-organisms to grow in the presence of a chemical (drug) that would normally kill them or limit their growth. As a result of antimicrobial resistance, existing antibiotics become less and less effective in eliminating infections caused by these micro-organisms. One of the ways to address this issue is to develop new antibiotics. This paper discusses the potential of sourcing antimicrobial compounds from a marine alga, Turbinaria ornata. To test the antimicrobial properties of the marine alga’s extract, a chemical indicator, resazurin was used. There are two methods of using resazurin to indicate antimicrobial properties; the authors used both methods and tried to analyze if the two methods were agreeable to each other.

Competing Interests

The authors declare no competing interest.

Acknowledgements

The authors would also like to thank Mr. Lee Ser Yong for helping with the water extraction of T. ornata and assays. We also appreciate the kindness of Dr. Chong Chun Wie and Ms. Tsen Min Tze for providing assistance in statistical analysis.

Additional information

Notes on contributors

Kar-Yee Tye

The main focus of our research is the exploration of natural resources for drugs and natural products. Natural products have played important roles in drug development for medicine and health. We are involved in sourcing plant and algal bioactive compounds with properties such as antioxidative, anti-neuroinflammatory, antifungal, antimicrobial as well as neuroprotective. Our research scopes include toxicology and neurodegenerative disorders. In addition, we are also involved in various molecular studies to understand the biological effects of the compounds using both animal models and in vitro cell-based assays.