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Comparison of methods to detect the in vitro activity of silver nanoparticles (AgNP) against multidrug resistant bacteria.

Cavassin ED, de Figueiredo LF, Otoch JP, Seckler MM, de Oliveira RA, Franco FF, Marangoni VS, Zucolotto V, Levin AS, Costa SF - J Nanobiotechnology (2015)

Bottom Line: 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 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.

View Article: PubMed Central - PubMed

Affiliation: Department of Infectious Diseases, University of São Paulo, São Paulo, Brazil. emerson_danguy@yahoo.com.br.

ABSTRACT

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.

No MeSH data available.


Related in: MedlinePlus

FEG-SEM micrographs of AgNPs stabilized by a PVA, b chitosan and c citrate
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Fig1: FEG-SEM micrographs of AgNPs stabilized by a PVA, b chitosan and c citrate

Mentions: The size and morphology of the AgNPs were investigated by Field Emission Gun Scanning Electron Microscope–FEG-SEM (Fig. 1). PVA-AgNPs and Chitosan-AgNPs presented an average diameter around 10 and 25 nm, respectively, while the citrate-AgNPs have around 40 nm of diameter. The UV–VIS spectra in Fig. 2 show the optical properties of PVA, Chitosan and Citrate stabilized AgNPs. The results reveal the surface plasmon resonances peaks around 400 nm for all systems, which is typical for nanostructured silver [15–17]. It is well known that the surface plasmon resonances depend strongly on the size, shape and functionalization of the metallic NPs [18]. The increasing in the size of the AgNPs leads to a red-shift and broadening of the plasmon resonance band [18], which agree with the spectrum observed for Citrate-AgNPs. The zeta potential analysis reveals significant differences in the surface charges between the three systems (Table 1). Chitosan AgNPs presented high positively surface charge (+41.1 mV), while the citrate ones were very negative (−48.4 mV) and PVA AgNPs were more close to zero (−17.0 mV).Fig. 1


Comparison of methods to detect the in vitro activity of silver nanoparticles (AgNP) against multidrug resistant bacteria.

Cavassin ED, de Figueiredo LF, Otoch JP, Seckler MM, de Oliveira RA, Franco FF, Marangoni VS, Zucolotto V, Levin AS, Costa SF - J Nanobiotechnology (2015)

FEG-SEM micrographs of AgNPs stabilized by a PVA, b chitosan and c citrate
© Copyright Policy - OpenAccess
Related In: Results  -  Collection

License 1 - License 2
Show All Figures
getmorefigures.php?uid=PMC4593215&req=5

Fig1: FEG-SEM micrographs of AgNPs stabilized by a PVA, b chitosan and c citrate
Mentions: The size and morphology of the AgNPs were investigated by Field Emission Gun Scanning Electron Microscope–FEG-SEM (Fig. 1). PVA-AgNPs and Chitosan-AgNPs presented an average diameter around 10 and 25 nm, respectively, while the citrate-AgNPs have around 40 nm of diameter. The UV–VIS spectra in Fig. 2 show the optical properties of PVA, Chitosan and Citrate stabilized AgNPs. The results reveal the surface plasmon resonances peaks around 400 nm for all systems, which is typical for nanostructured silver [15–17]. It is well known that the surface plasmon resonances depend strongly on the size, shape and functionalization of the metallic NPs [18]. The increasing in the size of the AgNPs leads to a red-shift and broadening of the plasmon resonance band [18], which agree with the spectrum observed for Citrate-AgNPs. The zeta potential analysis reveals significant differences in the surface charges between the three systems (Table 1). Chitosan AgNPs presented high positively surface charge (+41.1 mV), while the citrate ones were very negative (−48.4 mV) and PVA AgNPs were more close to zero (−17.0 mV).Fig. 1

Bottom Line: 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 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.

View Article: PubMed Central - PubMed

Affiliation: Department of Infectious Diseases, University of São Paulo, São Paulo, Brazil. emerson_danguy@yahoo.com.br.

ABSTRACT

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.

No MeSH data available.


Related in: MedlinePlus