| 1. |
- Alarcon, Emilio I, et al.
(författare)
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The biocompatibility and antibacterial properties of collagen-stabilized, photochemically prepared silver nanoparticles
- 2012
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Ingår i: Biomaterials. - : Elsevier. - 0142-9612 .- 1878-5905. ; 33:19, s. 4947-4956
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Tidskriftsartikel (refereegranskat)abstract
- Spherical 3.5 nm diameter silver nanoparticles (AgNP) stabilized in type I collagen (AgNP@collagen) were prepared in minutes (5-15 min) at room temperature by a photochemical method initiated by UVA irradiation of a water-soluble non-toxic benzoin. This biocomposite was examined to evaluate its biocompatibility and its anti-bacterial properties and showed remarkable properties. Thus, while keratinocytes and fibroblasts were not affected by AgNP@collagen, it was bactericidal against Bacillus megaterium and E. coli but only bacteriostatic against S. epidermidis. In particular, the bactericidal properties displayed by AgNP@collagen were proven to be due to AgNP in AgNP@collagen, rather than to released silver ions, since equimolar concentrations of Ag are about four times less active than AgNP@collagen based on total Ag content. This new biocomposite was stable over a remarkable range of NaCl, phosphate, and 2-(N-morpholino)ethanesulfonic acid concentrations and for over one month at 4 degrees C. Circular dichroism studies show that the conformation of collagen in AgNP@collagen remains intact. Finally, we have compared the properties of AgNP@collagen with a similar biocomposite prepared using alpha-poly-L-Lysine and also with citrate stabilized AgNP; neither of these materials showed comparable biocompatibility, stability, or anti-bacterial activity.
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| 2. |
- Nielsen, Karen L., et al.
(författare)
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Fitness cost : a bacteriological explanation for the demise of the first international methicillin-resistant Staphylococcus aureus epidemic
- 2012
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Ingår i: Journal of Antimicrobial Chemotherapy. - : Oxford University Press (OUP). - 0305-7453 .- 1460-2091. ; 67:6, s. 1325-1332
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Tidskriftsartikel (refereegranskat)abstract
- Denmark and several other countries experienced the first epidemic of methicillin-resistant Staphylococcus aureus (MRSA) during the period 196575, which was caused by multiresistant isolates of phage complex 83A. In Denmark these MRSA isolates disappeared almost completely, being replaced by other phage types, predominantly only penicillin resistant. We investigated whether isolates of this epidemic were associated with a fitness cost, and we employed a mathematical model to ask whether these fitness costs could have led to the observed reduction in frequency. Bacteraemia isolates of S. aureus from Denmark have been stored since 1957. We chose 40 S. aureus isolates belonging to phage complex 83A, clonal complex 8 based on spa type, ranging in time of isolation from 1957 to 1980 and with varyous antibiograms, including both methicillin-resistant and -susceptible isolates. The relative fitness of each isolate was determined in a growth competition assay with a reference isolate. Significant fitness costs of 215 were determined for the MRSA isolates studied. There was a significant negative correlation between number of antibiotic resistances and relative fitness. Multiple regression analysis found significantly independent negative correlations between fitness and the presence of mecA or streptomycin resistance. Mathematical modelling confirmed that fitness costs of the magnitude carried by these isolates could result in the disappearance of MRSA prevalence during a time span similar to that seen in Denmark. We propose a significant fitness cost of resistance as the main bacteriological explanation for the disappearance of the multiresistant complex 83A MRSA in Denmark following a reduction in antibiotic usage.
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| 3. |
- Udekwu, Klas I.
(författare)
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Transcriptional and Post-Transcriptional Regulation of the Escherichia coli luxS mRNA : Involvement of the sRNA MicA
- 2010
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Ingår i: PloS one. - : Public Library of Science (PLoS). - 1932-6203. ; 5:10, s. e13449-
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Tidskriftsartikel (refereegranskat)abstract
- Background: The small RNA (sRNA) MicA has been shown to post-transcriptionally regulate translation of the outer membrane protein A (OmpA) in Escherichia coli. It uses an antisense mechanism to down-regulate OmpA protein synthesis and induce mRNA degradation. MicA is genomically localized between the coding regions of the gshA and luxS genes and is divergently transcribed from its neighbours. Transcription of the luxS gene which originates within or upstream of the MicA sequence would thus be complementary to the sRNA. LuxS regulation is as yet unclear. Methodology/Principal Findings: In this report, I show that the luxS mRNA exists as three long (major) transcripts of sizes that suggest just such interaction. The sRNA MicA's expression affects the abundance of each of these luxS transcripts. The involvement of the ribonuclease, RNase III in the accumulation of the shortest transcript is demonstrated. When MicA accumulates during growth, or is induced to be over-expressed, the cleaved mRNA species is observed to increase in intensity. Using primer extension and 5'-RACE experiments in combination with sRNA overexpression plasmids, I identify the exact origin of two of the three luxS transcripts, one of which is seen to result from a previously unidentified sigma(5) dependent promoter. Conclusions/Significance: The presented data provides strong evidence that MicA functions in cis and in trans, targeting both luxS mRNA as well as the previously established ompA and phoP regulation. The proposed luxS regulation by MicA would be in tandem with another sRNA CyaR, shown recently to be involved in inhibiting translation of the luxS mRNA. Regulation of luxS expression is additionally shown to occur on a transcriptional level via sigma(5) with variable transcript levels in different growth phases unlike what was previously assumed. This is the first known case of an sRNA in E. coli which targets both in cis (luxS mRNA) and in trans (ompA and phoP mRNAs).
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