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Updated: Apr 1, 2026
Evaluation of Antimicrobial Activities of Nanoparticles and Nanostructured Surfaces In Vitro
Published on: April 21, 2023
Comparison of methods to detect the in vitro activity of silver nanoparticles (AgNP) against multidrug resistant
Emerson Danguy Cavassin1, Luiz Francisco Poli de Figueiredo2, José Pinhata Otoch3
1Department of Infectious Diseases, University of São Paulo, São Paulo, Brazil. emerson_danguy@yahoo.com.br.
Background:
Multidrug resistant microorganisms are a growing challenge and new substances that can be useful to treat infections due to these microorganisms are needed. Silver nanoparticle may be a future option for treatment of these infections, however, the methods described in vitro to evaluate the inhibitory effect are controversial.
Results:
This study evaluated the in vitro activity of silver nanoparticles against 36 susceptible and 54 multidrug resistant Gram-positive and Gram-negative bacteria from clinical sources. The multidrug resistant bacteria were oxacilin-resistant Staphylococcus aureus, vancomycin-resistant Enterococcus spp., carbapenem- and polymyxin B-resistant A. baumannii, carbapenem-resistant P. aeruginosa and carbapenem-resistant Enterobacteriaceae. We analyzed silver nanoparticles stabilized with citrate, chitosan and polyvinyl alcohol and commercial silver nanoparticle. Silver sulfadiazine and silver nitrate were used as control. Different methods were used: agar diffusion, minimum inhibitory concentration, minimum bactericidal concentration and time-kill. The activity of AgNPs using diffusion in solid media and the MIC methods showed similar effect against MDR and antimicrobial-susceptible isolates, with a higher effect against Gram-negative isolates. The better results were achieved with citrate and chitosan silver nanoparticle, both with MIC90 of 6.75 μg mL(-1), which can be due the lower stability of these particles and, consequently, release of Ag(+) ions as revealed by X-ray diffraction (XRD). The bactericidal effect was higher against antimicrobial-susceptible bacteria.
Conclusion:
It seems that agar diffusion method can be used as screening test, minimum inhibitory concentration/minimum bactericidal concentration and time kill showed to be useful methods. The activity of commercial silver nanoparticle and silver controls did not exceed the activity of the citrate and chitosan silver nanoparticles. The in vitro inhibitory effect was stronger against Gram-negative than Gram-positive, and similar against multidrug resistant and susceptible bacteria, with best result achieved using citrate and chitosan silver nanoparticles. The bactericidal effect of silver nanoparticle may, in the future, be translated into important therapeutic and clinical options, especially considering the shortage of new antimicrobials against the emerging antimicrobial resistant microorganisms, in particular against Gram-negative bacteria.
Insights
Silver nanoparticles show promise for treating multidrug-resistant infections, particularly against Gram-negative bacteria. Citrate and chitosan-stabilized silver nanoparticles demonstrated superior in vitro activity compared to commercial versions and controls.
Area of Science:
- Nanotechnology
- Microbiology
- Infectious Diseases
Background:
- Multidrug-resistant (MDR) microorganisms pose a significant global health threat.
- Novel antimicrobial agents are urgently needed to combat resistant bacterial infections.
- Silver nanoparticles (AgNPs) are being investigated as potential therapeutic agents.
Purpose of the Study:
- To evaluate the in vitro antimicrobial activity of different silver nanoparticles (AgNPs).
- To compare the efficacy of AgNPs against both susceptible and multidrug-resistant bacteria.
- To assess various in vitro methods for evaluating AgNP antimicrobial effects.
Main Methods:
- Tested AgNPs stabilized with citrate, chitosan, and polyvinyl alcohol, plus a commercial AgNP.
- Included silver sulfadiazine and silver nitrate as controls.
- Employed agar diffusion, minimum inhibitory concentration (MIC), minimum bactericidal concentration (MBC), and time-kill assays.
Main Results:
- AgNPs exhibited inhibitory activity against both susceptible and MDR Gram-positive and Gram-negative bacteria.
- Citrate and chitosan AgNPs showed the best performance, with an MIC90 of 6.75 μg/mL.
- In vitro activity was greater against Gram-negative than Gram-positive bacteria.
- Bactericidal effects were more pronounced against antimicrobial-susceptible bacteria.
Conclusions:
- Agar diffusion can serve as an effective initial screening method for AgNP activity.
- MIC/MBC and time-kill assays are valuable for detailed evaluation of AgNP efficacy.
- Citrate and chitosan AgNPs outperformed commercial AgNPs and silver salt controls.
- AgNPs, particularly against Gram-negative MDR bacteria, represent a promising future therapeutic option given the limited availability of new antibiotics.
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