Mycosynthesis of AgNPs: mechanisms of nanoparticle formation and antimicrobial activities

The inactivation and eradication of multidrug-resistant bacteria, fungi, and viruses by conventional antibiotics and drugs have not been effective. The hindering of these pathogens in hospital-acquired infections caused by Gram-positive bacteria, particularly strains of S. aureus including community-acquired methicillin-resistant (CA-MRSA) and hospital-acquired MRSA (HA-MRSA), is more complicated, specifically in patients having immunodeficiency syndrome.Bare and functionalized metal and metal oxide nanoparticles (NPs) specifically silver (Ag) NPs have shown significant antibacterial, antifungal, and antiviral activities. Biosynthesis of AgNPs by fungal species in media of cell-free filtrate and culture supernatant can provide new therapeutic properties compared to physical and chemical methods.Various primary and secondary metabolites of fungi such as phytochelatin, trichodin, primin, altersolanol A, periconicin A, brefeldin A, graphislactone A, phomol, polysaccharides (chitin, glucans, and galactomannans), and enzymes can contribute to reducing Ag+ ions and stabilizing NPs in one-pot method. These natural compounds can augment antimicrobial activity by bypassing multidrug-resistance barriers in viruses, bacteria, and fungi. Controlling physicochemical properties and effective therapeutic concentration of fungal AgNPs can be the determinative parameters for the antimicrobial strength of AgNPs. Therefore, in this review, we have tried to address the antimicrobial mechanisms and physicochemical properties of fungal synthesized AgNPs.