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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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Related in: MedlinePlus

Growth curves of S. aureus (a) and P. aeruginosa (b) under the influence of the dressing extracts determined by MLN. It was found that extracts of silver-free dressings did not affect the growth of S. aureus and P. aeruginosa in solution. Extracts of silver-containing alginates effectively diminished bacterial growth, while CMC with Ag+ and PU-foam with TLC/Ag+ were only able to inhibit S. aureus and P. aeruginosa progeny
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Fig2: Growth curves of S. aureus (a) and P. aeruginosa (b) under the influence of the dressing extracts determined by MLN. It was found that extracts of silver-free dressings did not affect the growth of S. aureus and P. aeruginosa in solution. Extracts of silver-containing alginates effectively diminished bacterial growth, while CMC with Ag+ and PU-foam with TLC/Ag+ were only able to inhibit S. aureus and P. aeruginosa progeny

Mentions: Microplate laser nephelometry (MLN) was used to monitor the growth of S. aureus (Fig. 2a) and P. aeruginosa (Fig. 2b) under the influence of the dressing extracts. In accordance to the ADT, a bactericidal effect was only observed in the case of the silver-containing dressings. The antibacterial activity of the extracts further depended on the extractability of the silver in the dressings. A complete inhibition of S. aureus and P. aeruginosa growth was achieved by extracts of alginate + ionic-Ag and alginate + nano-Ag. The extract of CMC with Ag+ demonstrated a significant reduction of S. aureus growth; however, silver concentrations reached were not high enough to abolish P. aeruginosa progeny. In contrast, extract of PU-foam with TLC/Ag+ accomplished a higher effect against P. aeruginosa compared to S. aureus.Fig. 2


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)

Growth curves of S. aureus (a) and P. aeruginosa (b) under the influence of the dressing extracts determined by MLN. It was found that extracts of silver-free dressings did not affect the growth of S. aureus and P. aeruginosa in solution. Extracts of silver-containing alginates effectively diminished bacterial growth, while CMC with Ag+ and PU-foam with TLC/Ag+ were only able to inhibit S. aureus and P. aeruginosa progeny
© Copyright Policy - OpenAccess
Related In: Results  -  Collection

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

Fig2: Growth curves of S. aureus (a) and P. aeruginosa (b) under the influence of the dressing extracts determined by MLN. It was found that extracts of silver-free dressings did not affect the growth of S. aureus and P. aeruginosa in solution. Extracts of silver-containing alginates effectively diminished bacterial growth, while CMC with Ag+ and PU-foam with TLC/Ag+ were only able to inhibit S. aureus and P. aeruginosa progeny
Mentions: Microplate laser nephelometry (MLN) was used to monitor the growth of S. aureus (Fig. 2a) and P. aeruginosa (Fig. 2b) under the influence of the dressing extracts. In accordance to the ADT, a bactericidal effect was only observed in the case of the silver-containing dressings. The antibacterial activity of the extracts further depended on the extractability of the silver in the dressings. A complete inhibition of S. aureus and P. aeruginosa growth was achieved by extracts of alginate + ionic-Ag and alginate + nano-Ag. The extract of CMC with Ag+ demonstrated a significant reduction of S. aureus growth; however, silver concentrations reached were not high enough to abolish P. aeruginosa progeny. In contrast, extract of PU-foam with TLC/Ag+ accomplished a higher effect against P. aeruginosa compared to S. aureus.Fig. 2

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