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In vitro assessment of the antimicrobial activity of wound dressings: influence of the test method selected and impact of the pH.

Wiegand C, Abel M, Ruth P, Elsner P, Hipler UC - J Mater Sci Mater Med (2015)

Bottom Line: They did not exhibit any antimicrobial effects in the ADT, MLN or LQbATP, since these methods depend on diffusion/extraction of an active agent.However, they showed a strong antimicrobial effect in the challenge tests as they possess a high absorptive capacity, and are able to bind and sequester micro-organisms present.Therefore, it seems recommendable to choose several tests to distinguish whether a material conveys an active effect or a passive mechanism.

View Article: PubMed Central - PubMed

Affiliation: Department of Dermatology, University Hospital Center Jena, Erfurter Str. 35, 07740, Jena, Germany, C.Wiegand@med.uni-jena.de.

ABSTRACT
Antibacterial activity of dressings containing antimicrobials is mostly evaluated using in vitro tests. However, the various methods available differ significantly in their properties and results obtained are influenced by the method selected, micro-organisms used, and extraction method, the degree of solubility or the diffusability of the test-compounds. Here, results on antimicrobial activity of silver-containing dressings obtained by agar diffusion test (ADT), challenge tests (JIS L 1902, AATCC 100), and extraction-based methods (microplate laser nephelometry (MLN), luminescent quantification of bacterial ATP (LQbATP)) using Staphylococcus aureus and Pseudomonas aeruginosa were evaluated. Furthermore, the effect of the pH on antibacterial efficacy of these dressings was investigated. All silver-containing dressings exerted antimicrobial activity in all in vitro tests and results correlated considerably well. Differences were observed testing the agent-free basic materials. They did not exhibit any antimicrobial effects in the ADT, MLN or LQbATP, since these methods depend on diffusion/extraction of an active agent. However, they showed a strong antimicrobial effect in the challenge tests as they possess a high absorptive capacity, and are able to bind and sequester micro-organisms present. Therefore, it seems recommendable to choose several tests to distinguish whether a material conveys an active effect or a passive mechanism. In addition, it could be shown that release of silver and its antimicrobial efficacy is partially pH-dependent, and that dressings themselves affect the pH. It can further be speculated that dressings' effects on pH and release of silver ions act synergistically for antimicrobial efficacy.

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For determination of the pH influence on antibacterial efficacy using the ADT, caso-agar plates with different pH were inoculated with S. aureus (a) or P. aeruginosa (b) and incubated with the silver-containing dressings at 37 °C for 24 h. Subsequently, the zone of inhibition (ZOI) was measured
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Fig4: For determination of the pH influence on antibacterial efficacy using the ADT, caso-agar plates with different pH were inoculated with S. aureus (a) or P. aeruginosa (b) and incubated with the silver-containing dressings at 37 °C for 24 h. Subsequently, the zone of inhibition (ZOI) was measured

Mentions: For testing the effect of the pH on antibacterial efficacy in the ADT, caso-agar plates with pH 5.0, 6.0, 7.0, 8.0, and 9.0 were inoculated with S. aureus (Fig. 4a) or P. aeruginosa (Fig. 4b). Alginate + nano-Ag caused an average ZOI of 10 mm and was equally effective against S. aureus and P. aeruginosa. No change in the antibacterial effect was further observed for PU-foam with TLC/Ag+ at the different pH. In contrast, CMC with Ag+ exhibited an increased ZOI against S. aureus at pH 9.0 and against P. aeruginosa at both, pH 5.0 and pH 9.0. Interestingly, alginate + ionic-Ag did not reveal a pH-dependency of the ZOI formation in the test against S. aureus. However, against P. aeruginosa a significant increase of the antibacterial effect from pH 5.0 to pH 9.0 was observed for alginate + ionic-Ag.Fig. 4


In vitro assessment of the antimicrobial activity of wound dressings: influence of the test method selected and impact of the pH.

Wiegand C, Abel M, Ruth P, Elsner P, Hipler UC - J Mater Sci Mater Med (2015)

For determination of the pH influence on antibacterial efficacy using the ADT, caso-agar plates with different pH were inoculated with S. aureus (a) or P. aeruginosa (b) and incubated with the silver-containing dressings at 37 °C for 24 h. Subsequently, the zone of inhibition (ZOI) was measured
© Copyright Policy - OpenAccess
Related In: Results  -  Collection

Show All Figures
getmorefigures.php?uid=PMC4325976&req=5

Fig4: For determination of the pH influence on antibacterial efficacy using the ADT, caso-agar plates with different pH were inoculated with S. aureus (a) or P. aeruginosa (b) and incubated with the silver-containing dressings at 37 °C for 24 h. Subsequently, the zone of inhibition (ZOI) was measured
Mentions: For testing the effect of the pH on antibacterial efficacy in the ADT, caso-agar plates with pH 5.0, 6.0, 7.0, 8.0, and 9.0 were inoculated with S. aureus (Fig. 4a) or P. aeruginosa (Fig. 4b). Alginate + nano-Ag caused an average ZOI of 10 mm and was equally effective against S. aureus and P. aeruginosa. No change in the antibacterial effect was further observed for PU-foam with TLC/Ag+ at the different pH. In contrast, CMC with Ag+ exhibited an increased ZOI against S. aureus at pH 9.0 and against P. aeruginosa at both, pH 5.0 and pH 9.0. Interestingly, alginate + ionic-Ag did not reveal a pH-dependency of the ZOI formation in the test against S. aureus. However, against P. aeruginosa a significant increase of the antibacterial effect from pH 5.0 to pH 9.0 was observed for alginate + ionic-Ag.Fig. 4

Bottom Line: They did not exhibit any antimicrobial effects in the ADT, MLN or LQbATP, since these methods depend on diffusion/extraction of an active agent.However, they showed a strong antimicrobial effect in the challenge tests as they possess a high absorptive capacity, and are able to bind and sequester micro-organisms present.Therefore, it seems recommendable to choose several tests to distinguish whether a material conveys an active effect or a passive mechanism.

View Article: PubMed Central - PubMed

Affiliation: Department of Dermatology, University Hospital Center Jena, Erfurter Str. 35, 07740, Jena, Germany, C.Wiegand@med.uni-jena.de.

ABSTRACT
Antibacterial activity of dressings containing antimicrobials is mostly evaluated using in vitro tests. However, the various methods available differ significantly in their properties and results obtained are influenced by the method selected, micro-organisms used, and extraction method, the degree of solubility or the diffusability of the test-compounds. Here, results on antimicrobial activity of silver-containing dressings obtained by agar diffusion test (ADT), challenge tests (JIS L 1902, AATCC 100), and extraction-based methods (microplate laser nephelometry (MLN), luminescent quantification of bacterial ATP (LQbATP)) using Staphylococcus aureus and Pseudomonas aeruginosa were evaluated. Furthermore, the effect of the pH on antibacterial efficacy of these dressings was investigated. All silver-containing dressings exerted antimicrobial activity in all in vitro tests and results correlated considerably well. Differences were observed testing the agent-free basic materials. They did not exhibit any antimicrobial effects in the ADT, MLN or LQbATP, since these methods depend on diffusion/extraction of an active agent. However, they showed a strong antimicrobial effect in the challenge tests as they possess a high absorptive capacity, and are able to bind and sequester micro-organisms present. Therefore, it seems recommendable to choose several tests to distinguish whether a material conveys an active effect or a passive mechanism. In addition, it could be shown that release of silver and its antimicrobial efficacy is partially pH-dependent, and that dressings themselves affect the pH. It can further be speculated that dressings' effects on pH and release of silver ions act synergistically for antimicrobial efficacy.

Show MeSH
Related in: MedlinePlus