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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

The specific IC50, the half maximum inhibitory concentrations, were calculated from the dose–response curves recorded at different pH for the extracts of alginate + ionic-Ag (a ), alginate + nano-Ag (b), CMC with Ag+ (c) and PU-foam with TLC/Ag+ (d) using MLN
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Fig5: The specific IC50, the half maximum inhibitory concentrations, were calculated from the dose–response curves recorded at different pH for the extracts of alginate + ionic-Ag (a ), alginate + nano-Ag (b), CMC with Ag+ (c) and PU-foam with TLC/Ag+ (d) using MLN

Mentions: It was found that low pH (5.0) already effectively inhibited microbial growth in solution. While no significant difference in the growth of S. aureus and P. aeruginosa was observed at pH 6.0–9.0, their progeny at pH 5.0 was found to be reduced to less than 10 % of the control at pH 7.0 (own unpublished results). Hence, MLN tests were only performed at a pH range of 6.0–9.0. It could be shown that the silver-dressing extracts possess a pH-dependent antimicrobial activity. For instance, IC50 values of the extracts of PU-foam with TLC/Ag+ significantly decreased from pH 6.0 to pH 9.0 against both, S. aureus and P. aeruginosa (Fig. 5d). Alginate + ionic-Ag also exhibited an increase in antibacterial activity for P. aeruginosa while IC50 values for S. aureus slightly increased from pH 6.0 to pH 8.0 and then again dropped at pH 9.0 (Fig. 5a). In addition, alginate + nano-Ag (Fig. 5b) and CMC with Ag+ (Fig. 5c) showed similar effects against S. aureus and P. aeruginosa demonstrating a reduction in IC50 values with increasing pH from 7.0 to 9.0. In both cases, a significantly higher antibacterial activity of the extracts was observed at pH 6.0.Fig. 5


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)

The specific IC50, the half maximum inhibitory concentrations, were calculated from the dose–response curves recorded at different pH for the extracts of alginate + ionic-Ag (a ), alginate + nano-Ag (b), CMC with Ag+ (c) and PU-foam with TLC/Ag+ (d) using MLN
© Copyright Policy - OpenAccess
Related In: Results  -  Collection

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

Fig5: The specific IC50, the half maximum inhibitory concentrations, were calculated from the dose–response curves recorded at different pH for the extracts of alginate + ionic-Ag (a ), alginate + nano-Ag (b), CMC with Ag+ (c) and PU-foam with TLC/Ag+ (d) using MLN
Mentions: It was found that low pH (5.0) already effectively inhibited microbial growth in solution. While no significant difference in the growth of S. aureus and P. aeruginosa was observed at pH 6.0–9.0, their progeny at pH 5.0 was found to be reduced to less than 10 % of the control at pH 7.0 (own unpublished results). Hence, MLN tests were only performed at a pH range of 6.0–9.0. It could be shown that the silver-dressing extracts possess a pH-dependent antimicrobial activity. For instance, IC50 values of the extracts of PU-foam with TLC/Ag+ significantly decreased from pH 6.0 to pH 9.0 against both, S. aureus and P. aeruginosa (Fig. 5d). Alginate + ionic-Ag also exhibited an increase in antibacterial activity for P. aeruginosa while IC50 values for S. aureus slightly increased from pH 6.0 to pH 8.0 and then again dropped at pH 9.0 (Fig. 5a). In addition, alginate + nano-Ag (Fig. 5b) and CMC with Ag+ (Fig. 5c) showed similar effects against S. aureus and P. aeruginosa demonstrating a reduction in IC50 values with increasing pH from 7.0 to 9.0. In both cases, a significantly higher antibacterial activity of the extracts was observed at pH 6.0.Fig. 5

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