Mycosynthesis of AgNPs: mechanisms of nanoparticle formation and antimicrobial activities

ABSTRACT

Introduction

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.

Research area

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.

Expert opinion

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.

KEYWORDS:

• Metal and metal oxide NPs
• Multidrug-resistance barriers
• Hospital-acquired MRSA
• fungal AgNPs
• secondary metabolites of fungi

Article highlights

• Antibiotic-resistant bacteria can be inactivated by suitable doses of metal NPs

• The antibacterial activity of metal NPs is changed by the alteration of physicochemical properties of NPs

• Compared to other metal NPs, AgNPs have more antibacterial activity against multidrug-resistant bacteria

• AgNP biosynthesis and stabilization by metabolites of bacteria and fungi have obtained enormous attention

• In fungi and bacteria, silver resistance mechanisms are critical to reduce and stabilizing Ag⁺ ions at concentration less than threshold limit

• Finding effective doses, shapes, and sizes of AgNPs with higher bactericidal effects and lower cytotoxicity is a critical issue to formulate future drugs

• Metabolites of bacteria and fungi can increase the biocompatibility, bioavailability, and biodegradability of AgNPs

Declaration of interest

The authors have no relevant affiliations or financial involvement with any organization or entity with a financial interest in or financial conflict with the subject matter or material discussed in the manuscript. This includes employment, consultancies, honoraria, stock ownership or options, expert testimony, grants or patents received or mending, or royalties.

Reviewer disclosures

Peer reviewers on this manuscript have no relevant financial or other relationships to disclose.

Additional information

Funding

This paper was not funded.