Extracellular Synthesis and Characterization of Silver Nanoparticles—Antibacterial Activity against Multidrug-Resistant Bacterial Strains

Abstract

Herein, we report the use of a cell-free extract for the extracellular synthesis of silver nanoparticles (AgNPs) and their potential to address the growing threat of multidrug-resistant (MDR) pathogenic bacteria. The reproducibility of AgNP synthesis was good and AgNP formation kinetics were monitored as a function of various reaction factors via ultraviolet-visible absorption spectroscopy. This green method was dependent on the alkaline pH of the reaction mixture. With the addition of dilute sodium hydroxide, well-dispersed AgNPs could be produced in large quantities via the classical nucleation and growth route. The new biosynthetic route enabled the production of AgNPs within a narrow size range of 4 to 17 nm. The AgNPs were characterized using various techniques and their antibacterial activity against MDR pathogenic bacteria was evaluated. Field-emission scanning electron microscopic imaging revealed prominent morphological changes in Staphylococcus aureus cells due to mechanical damage, which led to cell death. Escherichia coli cells showed signs of contraction and intracellular fluid discharge as a consequence of disrupted cell membrane function. This new biologically-assisted extracellular strategy is potentially useful for the decontamination of surfaces and is expected to contribute to the development of new products containing AgNPs.

Boosting nanotoxicity to combat multidrug-resistant bacteria in pathophysiological environments

“…[22][23][24][25][26] Not only the increasing cases of multidrug-resistant (MDR) bacteria but also the lack of still effective and novel antibiotics represent an increasing socio-economic problem. [27][28][29] Here, hospital-acquired MDR bacteria such as Methicillin-resistant Staphylococcus aureus (MRSA), Salmonella enterica or Pseudomonas aeruginosa, and extended-spectrum b-lactamaseproducing Escherichia coli (ESBL-EC) are problematic in the clinics even in highly developed countries. 10,27,[30][31][32][33][34][35][36] Consequently, NMs are investigated as tools for diagnosis of bacteria, as antibiotic drug carriers and/or based on their antimicrobial activity, directly tested as novel nano-antibiotics.…”

“…[27][28][29] Here, hospital-acquired MDR bacteria such as Methicillin-resistant Staphylococcus aureus (MRSA), Salmonella enterica or Pseudomonas aeruginosa, and extended-spectrum b-lactamaseproducing Escherichia coli (ESBL-EC) are problematic in the clinics even in highly developed countries. 10,27,[30][31][32][33][34][35][36] Consequently, NMs are investigated as tools for diagnosis of bacteria, as antibiotic drug carriers and/or based on their antimicrobial activity, directly tested as novel nano-antibiotics. 4,[6][7][8][9][10]27,29,35,37 Antibacterial nano-therapeutics so far mainly focused on a variety of semiconductor, metal, and metal oxide NMs.…”

“…10,27,[30][31][32][33][34][35][36] Consequently, NMs are investigated as tools for diagnosis of bacteria, as antibiotic drug carriers and/or based on their antimicrobial activity, directly tested as novel nano-antibiotics. 4,[6][7][8][9][10]27,29,35,37 Antibacterial nano-therapeutics so far mainly focused on a variety of semiconductor, metal, and metal oxide NMs. 4,10,22,27,29,38,39 Here, their antibacterial properties seem to be mainly due to the release of toxic metal ions, physical damage of bacterial membranes, the generation of free radicals and reactive species, as well as by local heating through surface plasmon resonance effects.…”

“…4,[6][7][8][9][10]27,29,35,37 Antibacterial nano-therapeutics so far mainly focused on a variety of semiconductor, metal, and metal oxide NMs. 4,10,22,27,29,38,39 Here, their antibacterial properties seem to be mainly due to the release of toxic metal ions, physical damage of bacterial membranes, the generation of free radicals and reactive species, as well as by local heating through surface plasmon resonance effects. 10,29,[38][39][40] Moreover, anti-microbial nanopeptide polymers have been reported, potentially acting via membrane destabilization and damage.…”

“…4,69 The blood-system, the orogastrointestinal tract, lung as well as (skin) wound applications of NMs represent main targets for nano-antibiotics. 4,[6][7][8][9][10]27,29,[35][36][37] Notably, such (patho)physiological systems are oen highly dynamic and NMs are expected to contact bacteria only for a short period of time. However, most studies investigated rather articial static and constant treatment scenarios so far, oen neglecting the dynamics of bacteria-NM interaction.…”