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

摘要

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 (Ag NP s) was successfully accomplished in the presence of Eucalyptus citriodora leaf extract as a reducing agent. In this study, the antimicrobial mechanisms of Ag NP s against important hospital‐acquired pathogens, including Gram‐positive, Gram‐negative bacteria, and fungi were further assessed. The results indicated that Ag NP s 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 Ag NP s produced bactericidal effects on the microorganisms. Ag NP s could significantly reduce biofilm production in pathogens without affecting growth of the pathogens (p ? ? 0.05). Ag NP s inhibited cell viability and biofilm formation in a dose‐dependent manner. Cell membrane damage in microorganisms resulting from effects of Ag NP s was observed. A significant increase in per cent uptake of crystal violet was observed in all isolates treated with Ag NP s when compared with the control (p ? ? 0.05). Upon treatment with Ag NP s, the surface charge of the reference strains and clinical isolates of pathogens moved towards neutral. The alteration of surface potential after exposure to Ag NP s could contribute to membrane disruption and cell viability. Scanning electron microscopy further confirmed morphological cell changes and disrupted the cell membrane. Increasing resistance to Ag NP s was not induced by stepwise isolation of the bacteria after 45 passages on Luria‐Bertani agar supplemented with Ag NP s. Furthermore, Ag NP s was not toxic to red blood cells.