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Abstract
Introduction Medicinal utility of lichens is ascribed to the presence of various secondary metabolites of low molecular weight and they have been used in traditional medicine including Ayurveda in the treatment of wounds and skin disorders. Despite the urgent need to effectively address the antibiotic resistance worldwide, the discovery of new antibacterial drugs has declined in the recent past. This emphasizes the increasing importance of investigating and developing new classes of antibiotics that can withstand antibiotic resistance. Aims of the study. The present study was conducted to investigate the chemical composition and the antibacterial activity of hexane, ethanol, and aqueous extracts of Parmotrema rampoddense and Parmotrema tinctorum, two lichens collected from Belihuloya, Sri Lanka, against Gram-negative and Gram-positive bacteria including twenty clinical isolates of methicillin-resistant Staphylococcus aureus (MRSA). Materials and methods. Phytochemical analysis, thin layer chromatography (TLC), and Gas Chromatography Mass Spectrometry (GC-MS) were performed to determine the chemical composition of the two lichens. Hexane, ethanol, and aqueous extracts of both lichens were tested against clinical isolate of Gram-negative and Gram-positive bacteria including twenty clinical isolates of MRSA. Bacterial susceptibility was tested using a disc diffusion assay. Minimum inhibitory concentration (MIC) was determined by a broth microdilution method. Vancomycin was used as the positive control. Results Alectorialic acid, atranorin, atraric acid, orcinol, and O-orsellinaldehyde were among the secondary metabolites identified by the TLC and GC-MS analysis. None of the lichen extracts were active against Gram-negative bacteria but both lichens showed a concentration-dependent activity against methicillin-sensitive Staphylococcus aureus (MSSA) and MRSA. Ethanol extract of P. rampoddense showed the highest activity against MSSA with the MIC, 0.0192 mg/ml, but all MRSA isolates investigated showed MIC between 0.096 and 2.4 mg/ml for the same extract. Conclusion Both lichens, P. rampoddense and P. tinctorum, represent potentially important sources of future antimicrobial drugs. Further investigation on the ethanol extract of P. rampoddense will enable us to determine the most active phytoconstituents responsible for the activity, their mechanism of action against bacterial pathogens, and also their cytotoxicity against normal cells.
Highlights
Medicinal utility of lichens is ascribed to the presence of various secondary metabolites of low molecular weight and they have been used in traditional medicine including Ayurveda in the treatment of wounds and skin disorders
The chemical composition and antimicrobial activity of three different extracts of two Sri Lankan lichens, P. rampoddense and P. tinctorum were compared against methicillin-sensitive and methicillin-resistant S. aureus
Variation in the results reported for P. rampoddense and P. tinctorum between the two research groups may be due to a combination of factors, including the extraction of different lichen species, type of extract and its concentration, the solvent used for extraction, and the specific bacterial strain [45]. e differences in results between the two studies could be due to certain adaptations and modifications that could take place for the survival of the species in different climatic conditions and geographical locations
Summary
Medicinal utility of lichens is ascribed to the presence of various secondary metabolites of low molecular weight and they have been used in traditional medicine including Ayurveda in the treatment of wounds and skin disorders. E present study was conducted to investigate the chemical composition and the antibacterial activity of hexane, ethanol, and aqueous extracts of Parmotrema rampoddense and Parmotrema tinctorum, two lichens collected from Belihuloya, Sri Lanka, against Gram-negative and Gram-positive bacteria including twenty clinical isolates of methicillin-resistant Staphylococcus aureus (MRSA). Ethanol, and aqueous extracts of both lichens were tested against clinical isolate of Gram-negative and Gram-positive bacteria including twenty clinical isolates of MRSA. None of the lichen extracts were active against Gram-negative bacteria but both lichens showed a concentration-dependent activity against methicillin-sensitive Staphylococcus aureus (MSSA) and MRSA. Further investigation on the ethanol extract of P. rampoddense will enable us to determine the most active phytoconstituents responsible for the activity, their mechanism of action against bacterial pathogens, and their cytotoxicity against normal cells
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