Eucalyptus citriodora leaf extract‐mediated biosynthesis of silver nanoparticles: broad antimicrobial spectrum and mechanisms of action against hospital‐acquired pathogens

Abstract

Pathogen resistance to conventional antibiotics has become a serious clinical and public health problem, making the development of an alternative mean a very urgent issue. Recently, biosynthesis of silver nanoparticles (AgNPs) was successfully accomplished in the presence of Eucalyptus citriodora leaf extract as a reducing agent. In this study, the antimicrobial mechanisms of AgNPs against important hospital‐acquired pathogens, including Gram‐positive, Gram‐negative bacteria, and fungi were further assessed. The results indicated that AgNPs could enhance a broad antimicrobial spectrum against drug‐resistant organisms, with a range of minimum inhibitory concentration from 0.02 to 0.36 μg/mL. Time‐kill assay showed that AgNPs produced bactericidal effects on the microorganisms. AgNPs could significantly reduce biofilm production in pathogens without affecting growth of the pathogens (p < 0.05). AgNPs inhibited cell viability and biofilm formation in a dose‐dependent manner. Cell membrane damage in microorganisms resulting from effects of AgNPs was observed. A significant increase in per cent uptake of crystal violet was observed in all isolates treated with AgNPs when compared with the control (p < 0.05). Upon treatment with AgNPs, the surface charge of the reference strains and clinical isolates of pathogens moved towards neutral. The alteration of surface potential after exposure to AgNPs could contribute to membrane disruption and cell viability. Scanning electron microscopy further confirmed morphological cell changes and disrupted the cell membrane. Increasing resistance to AgNPs was not induced by stepwise isolation of the bacteria after 45 passages on Luria‐Bertani agar supplemented with AgNPs. Furthermore, AgNPs was not toxic to red blood cells.

Biologically rapid synthesized silver nanoparticles from aqueous Eucalyptus camaldulensis leaf extract: Effects on hyphal growth, hydrolytic enzymes, and biofilm formation in Candida albicans

“…The MIC and MFC ranged from 0.25 to 0.5 µg/ml and 0.5 to 1 µg/ml, respectively. A similar anti‐candidal activity of AgNPs synthesized from another species of Eucalyptus has been reported in our earlier work (Paosen et al, 2019). It is to be noted that E. camaldulensis is the most widespread species of eucalyptus and abundant of the leaf litters are available from paper manufacturers (Siramon et al, 2009).…”

“…The surface morphological changes in the yeast cells may indicate the interaction of bio‐AgNPs with the cell wall and cell membrane. Bio‐AgNPs from E. citriodora leaf extract inhibited biofilms in C. albicans due to the alteration of membrane surface charges of pathogenic fungi following the exposure to the nanoparticles, leading to membrane disruption (Paosen et al, 2019). The release of Ag + from AgNPs was demonstrated to react with the thiol group of protein portion, generally presented in microbial enzymes, such as glyceraldehyde‐3‐phosphate dehydrogenase and malate dehydrogenase, resulting in pathogen inactivation (Jiang et al, 2019).…”

In-vitro anticancer activity against Caco-2 cell line of colloidal nano silver synthesized using aqueous extract of Eucalyptus Camaldulensis leaves

“…Nevertheless, Eucalyptus camaldulensis leaves contain a wide range of bioactive compounds including saponins, tannins, flavonoids, carbohydrate and proteins [ 28 ], which play important roles as reducing and capping agent during the formation of nanoparticles [ 29 , 30 ]. There are many articles published on the synthesis of AgNPs using different species of Eucalyptus such as Eucalyptus corymbia [ 31 ], Eucalyptus globules [ 32 ], Eucalyptus critriodora [ 33 ], and Eucalyptus tereticornis [ 34 ] etc… But, few studies have been reported in the using of aqueous extract of Eucalyptus camaldulensis leaves for synthesis silver nanoparticles [ 30 ].…”

Polymeric nanoemulsions enriched with Eucalyptus citriodora essential oil

“…Eucalyptus citriodora belongs to the Myrtaceae family, and these species are known for the characteristics of their essential oils. It is known that the E. citriodora essential oil (ECEO) has a wide spectrum of biological activities, including herbicidal [3,4] , antifungal [5] , insecticide [6] , antioxidant [7,8] , antimicrobial [9,10] properties. However, the storage of EOs is a critical matter due to their sensitivity to heat, humidity and air, being subject to hydrolysis, oxidation, dehydration and isomerization reactions [11][12][13] .…”