Antimicrobial applications of lichens: secondary metabolites and green synthesis of silver nanoparticles: A review

Lichens produce a variety of unique extracellular secondary metabolites because these organisms are a life form comprising a complex symbiotic relationship between fungi and algae, which occur in many ecosystems. These compounds are present within the thallus and form crystals on the surface of the fungal hyphae. More than ۸۰۰ different secondary metabolites, such as usnic acid, norstictic acid, atranorin, salazinic acid, stictic acid, atranorin, and chloroatranorin have been identified in lichens, most of which are found exclusively in lichen species. In recent years, lichens have received much attention for pharmaceutical and phytochemical applications. Lichens and their secondary metabolites have been investigated for various pharmacological activity, including antimicrobial, antioxidant, antiviral, anticancer, antigenotoxic, anti-inflammatory, antipyretic, and analgesic effects. This review discusses recent progress and challenges related to the antimicrobial activity of lichens, focusing on secondary metabolites of the leading medical species of lichen and the green synthesis of silver nanoparticles and nanocomposites.

Keywords:

Antipyretic effect , Antimicrobial activity , Extensively drug-resistant , Green synthesis , Lichens , Secondary metabolites , Silver nanoparticles , Usnic acid