Effect of agitation on antimicrobial activity and release during in-vitro testing of antimicrobial wound care dressings

Examensarbete för masterexamen
Master Thesis
Biotechnology (MPBIO), MSc
Åkerman, Julia
The use of antimicrobial substances to combat microorganisms has been in practice for centuries. Louis Pasteur’s germ theory published in 1865 was the first scientific evidence of the link between microorganisms and infectious disease and brought the implementation of antisepsis into hospital routines. The interest in antiseptics diminished with the discovery and introduction of antibiotics in clinical treatment in the 1940s, but the emergence of antibiotic resistance during the past decades has revived the interest in antiseptic agents as treatment of infectious diseases. The aim of this thesis was to evaluate the antimicrobial effect and release kinetics of two commonly used antimicrobial substances (silver and PHMB) during in-vitro testing of antimicrobial wound dressings. Experiments with the active substance in solution as well as experiments with the active substance in the form of antimicrobial wound care dressings were performed. The antimicrobial effect was evaluated using a two-compartment model by determining the number of viable cell counts by standard plate count method. The silver release from wound care dressings was determined by ICP-OES analysis. The PHMB release was assessed with spectrophotometric measurements and a colorimetric method involving the anionic dye Eosin Y. The influence of agitation was evaluated at static conditions and at agitation rates of 50 and 100 rpm respectively. Experiments with active substance in solution against P. aeruginosa showed no influence of agitation on antimicrobial effect. Higher PHMB susceptibility was observed for S. aureus compared to P. aeruginosa, this could be coupled to the outer cell membrane present in gram-negative bacteria which may act as permeability barrier against the polymeric PHMB. In contrast, experiments involving wound care dressings showed a clear correlation between increased antimicrobial effect and increased agitation rates for P. aeruginosa. The contradictive results of the two types of experiments may be explained by the initial mixing of inoculated medium and antimicrobial agent for the experiments with active substance in solution. In the experiments involving wound care dressings no such mixing occurred and hence, the effect of agitation is likely to be greater. The silver release during incubation was similar in experiments performed at static conditions and agitation at 50 rpm, but a significantly higher silver release was detected when agitation at 100 rpm was employed. As no proper control sample was accessible, the amount PHMB released during incubation was not possible to determine with analytical methods available at MHC. Although the presence of interfering substances was indicated in performed measurements of PHMB concentration it could be concluded that agitation does not seem to greatly influence the amount PHMB released, even at higher agitation rates.
Livsvetenskaper , Kemi , Biologiska vetenskaper , Life Science , Chemical Sciences , Biological Sciences
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