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Effects of Silver-based Wound Dressings on the Bacterial Flora in Chronic Leg Ulcers and Its Susceptibility In vitro to Silver
Uppsala University, Disciplinary Domain of Medicine and Pharmacy, Faculty of Medicine, Department of Medical Sciences, Clinical Bacteriology.
Uppsala University, Disciplinary Domain of Medicine and Pharmacy, Faculty of Medicine, Department of Medical Sciences, Clinical Bacteriology.
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2012 (English)In: Acta Dermato-Venereologica, ISSN 0001-5555, E-ISSN 1651-2057, Vol. 92, no 1, 34-39 p.Article in journal (Refereed) Published
Abstract [en]

Silver-based dressings have been used extensively in wound management in recent years, but data on their antimicrobial activity in the clinical setting are limited. In order to explore their effects on chronic leg ulcer flora, 14 ulcers were cultured after at least 3 weeks treatment with Aquacel Ag (R) or Acticoat (R). Phenotypic and genetic silver resistance were investigated in a total of 56 isolates. Silver-based dressings had a limited effect on primary wound pathogens, which were present in 79% of the cultures before, and 71% after, treatment. One silver-resistant Enterobacter cloacae strain was identified (silver nitrate minimal inhibitory concentration (MIC)>512 mg/l, positive for silE, silS and silP). Further studies in vitro showed that inducible silver-resistance was more frequent in Enterobacteriaceae with cephalosporin-resistance and that silver nitrate had mainly a bacteriostatic effect on Staphylococcus aureus. Monitoring of silver resistance should be considered in areas where silver is used extensively.

Place, publisher, year, edition, pages
2012. Vol. 92, no 1, 34-39 p.
Keyword [en]
silver, silver-resistance, wound dressing, ESBL, derepressed mutant
National Category
Medical and Health Sciences
Identifiers
URN: urn:nbn:se:uu:diva-171444DOI: 10.2340/00015555-1170ISI: 000300388400007OAI: oai:DiVA.org:uu-171444DiVA: diva2:510895
Available from: 2012-03-19 Created: 2012-03-19 Last updated: 2017-12-07Bibliographically approved
In thesis
1. Aspects of Bacterial Resistance to Silver
Open this publication in new window or tab >>Aspects of Bacterial Resistance to Silver
2015 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

Bacterial resistance to antibiotics has increased rapidly within recent years, and it has become a serious threat to public health. Infections caused by multi-drug resistant bacteria entail higher morbidity, mortality, and a burden to health care systems. The use of biocides, including silver compounds, may affect the resistance to both biocides and antibiotics and, thereby, can be a driving factor in this development.

The aim of the following thesis was to investigate the frequency of silver resistance and the effects of silver exposure on bacterial populations being of clinical significance and from geographically different parts of the world. Furthermore, it explored the genetic background of silver resistance, and if silver could select directly or indirectly for antibiotic resistance.

By a range of methods, from culture in broth to whole genome sequencing, bacterial populations from humans, birds and from the environment were characterized.

The studies showed that sil genes, encoding silver resistance, occurred at a high frequency. Sil genes were found in 48 % of Enterobacter spp., in 41 % of Klebsiella spp. and in 21 % of all human Escherichia coli isolates with production of certain types of extended-spectrum beta-lactamases (CTX-M-14 and CTX-M-15). In contrast, silver resistance was not found in bird isolates or in bacterial species, such as Pseudomonas aeruginosa and Legionella spp., with wet environments as their natural habitat. One silver-resistant Enterobacter cloacae strain was isolated from a chronic leg ulcer after only three weeks of treatment with silver-based dressings. The in-vivo effects of these dressings were limited, and they failed to eradicate both Gram-positive and Gram-negative bacteria. The activity of silver nitrate in vitro was bacteriostatic on Gram-positive species such as S. aureus and bactericidal on Gram-negative species. In Enterobacteriaceae, sil genes were associated with silver resistance phenotypes in all but one case. Using whole genome sequencing, single nucleotide polymorphisms in the silS gene were discovered after silver exposure in isolates with expressed silver resistance. This resistance could co-select for resistance to beta-lactams, co-trimoxazole and gentamicin.

The findings of this thesis indicate that silver exposure may cause phenotypic silver resistance, and it may reduce the susceptibility to mainly beta-lactams and select for bacteria with resistance to clinically important antibiotics.

Place, publisher, year, edition, pages
Uppsala: Acta Universitatis Upsaliensis, 2015. 64 p.
Series
Digital Comprehensive Summaries of Uppsala Dissertations from the Faculty of Medicine, ISSN 1651-6206 ; 1084
Keyword
Antimicrobial resistance, Silver resistance
National Category
Infectious Medicine
Research subject
Clinical Bacteriology
Identifiers
urn:nbn:se:uu:diva-247472 (URN)978-91-554-9205-2 (ISBN)
Public defence
2015-05-08, Hörsal, Department of clinical microbiology, Dag Hammarskjölds väg 17, Uppsala, 13:00 (Swedish)
Opponent
Supervisors
Available from: 2015-04-15 Created: 2015-03-18 Last updated: 2015-04-17
2. Survival of infectious agents and detection of their resistance and virulence factors
Open this publication in new window or tab >>Survival of infectious agents and detection of their resistance and virulence factors
2015 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

In the first study, three different transport systems for bacteria were evaluated. The CLSI M40-A guideline was used to monitor the maintenance of both mono- and polymicrobial samples during a simulated transportation at room temperature that lasted 0-48 h. All systems were able to maintain the viability of all organisms for 24 h, but none of them could support all tested species after 48 h.  The most difficult species to recover was Neisseria gonorrhoeae, and in polymicrobial samples overgrowth was an observed problem. The aim of the second study was to study the presence of TSST-1 and three other important toxin genes in invasive isolates of Staphylococcus aureus collected during the years 2000-2012 at two tertiary hospitals. The genes encoding the staphylococcal toxins were detected by PCR, and whole-genome sequencing was used for analyzing the genetic relatedness between isolates. The results showed that the most common toxin was TSST-1, and isolates positive for this toxin exhibited a clear clonality independent of year and hospital. The typical patient was a male aged 55-74 years and with a bone or a joint infection. The third study was a clinical study of the effect of silver-based wound dressings on the bacterial flora in chronic leg ulcers. Phenotypic and genetic silver-resistance were investigated before and after topical silver treatment, by determining the silver nitrate MICs and by detecting sil genes with PCR. The silver-based dressings had a limited effect on primary wound pathogens, and the activity of silver nitrate on S. aureus was mainly bacteriostatic. A silver-resistant Enterobacter cloacae strain was identified after only three weeks of treatment, and cephalosporin-resistant members of the Enterobacteriaceae family were relatively prone to developed silver-resistance after silver exposure in vitro. The last study was undertaken in order to develop an easy-to-use method for simulating the laundering process of hospital textiles, and apply the method when evaluating the decontaminating efficacy of two different washing temperatures. The laundering process took place at professional laundries, and Enterococcus faecium was used as a bioindicator. The results showed that a lowering of the washing temperature from 70°C to 60°C did not affect the decontamination efficacy; the washing cycle alone reduced the number of bacteria with 3-5 log10 CFU, whereas the following tumble drying reduced the bacterial numbers with another 3-4 log10 CFU, yielding the same final result independent of the washing temperature. To ensure that sufficient textile hygiene is maintained, the whole laundering process needs to be monitored. The general conclusion is that all developmental work in the bacterial field requires time and a large strain collection.

Place, publisher, year, edition, pages
Uppsala: Acta Universitatis Upsaliensis, 2015. 48 p.
Series
Digital Comprehensive Summaries of Uppsala Dissertations from the Faculty of Medicine, ISSN 1651-6206 ; 1098
Keyword
Transportation system; swab; polymicrobial samples; Neisseria gonorrhoeae; bacteremia; exotoxins; Staphylococcus aureus; TSST-1; silver; silver resistance; wound dressing; sil genes; laundry; tumble drying; bacterial decontamination
National Category
Clinical Laboratory Medicine
Identifiers
urn:nbn:se:uu:diva-248786 (URN)978-91-554-9232-8 (ISBN)
Public defence
2015-05-28, Hörsalen, Klinisk Mikrobiologi, Dag Hammarskjöldsväg 17, Ing D1, Uppsala, 13:15 (Swedish)
Opponent
Supervisors
Available from: 2015-05-05 Created: 2015-04-08 Last updated: 2015-07-07

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Sütterlin, SusanneTano, EvaMelhus, Åsa

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