Chemical Composition and Antimicrobial Activity of Two Sri Lankan Lichens, Parmotrema rampoddense, and Parmotrema tinctorum against Methicillin-Sensitive and Methicillin-Resistant Staphylococcus aureus

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.

Isolation, Characterization, and Breast Cancer Cytotoxic Activity of Gyrophoric Acid from the Lichen Umbilicaria muhlenbergii

“…A qualitative analysis of two Sri Lankan extracts from the lichens Parmotrema tinctorum and Parmotrema rampoddense revealed the presence of saponins, flavonoids, and polyphenols [44]. Anthracene glycosides were present in P. tinctorum but not in P. rampoddense, whereas proteins, alkaloids, tannins, reducing sugars, cyanogenic glycosides, and cardenolide glycosides were absent from both lichen extracts [44]. The presence of phenols and alkaloids with strong bioactivities is also in agreement with the published literature [17,45,46].…”

“…Lichenochemical screening studies on the crude extract of U. muhlenbergii revealed the presence of alkaloids and phenols as major components, with tannins, saponins, and hydrocarbons present in smaller quantities, whereas flavonoids, terpenoids, proteins, and glycosides were not detected (data not shown). A qualitative analysis of two Sri Lankan extracts from the lichens Parmotrema tinctorum and Parmotrema rampoddense revealed the presence of saponins, flavonoids, and polyphenols [44]. Anthracene glycosides were present in P. tinctorum but not in P. rampoddense, whereas proteins, alkaloids, tannins, reducing sugars, cyanogenic glycosides, and cardenolide glycosides were absent from both lichen extracts [44].…”

Phenolic Secondary Metabolites and Antiradical and Antibacterial Activities of Different Extracts of Usnea barbata (L.) Weber ex F.H.Wigg from Călimani Mountains, Romania

“…Considering the data registered in Table 5 , we calculated the antibacterial activity index (AI), reporting the IZD values (mm) of lichen extracts to the ones of the standard antibiotic drugs [ 47 ]. It can be noted that dry and fluid U. barbata acetone and ethanol extracts had similar inhibitory effects ( Table 6 ).…”

“…The activity index (AI) [ 47 ] is calculated using the following formula: where IZD sample—inhibition zone diameter for each U. barbata extract, and IZD standard—inhibition zone diameter for each antibacterial drug, used as standard.…”

A review of the potential of lichen substances as antifungal agents: the effects of extracts and lichen secondary metabolites on Fusarium fungi

“…Laboratory in vitro studies on the potential of lichen secondary metabolites report their broad biological properties such as anticancer (Cardile et al 2017 ; Tripathi et al 2022 and literature cited therein), antioxidant (Hawrył et al 2020 ; Maulidiyah et al 2021 ), antimicrobial (Shiromi et al 2021 ; Sargsyan et al 2021 ), pro-health (Zhao et al 2021 and literature cited therein) or anti-fusarial potentials described in this meta-analysis.…”