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| 2. |
- Kugelberg, Elisabeth, et al.
(författare)
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Establishment of a superficial skin infection model in mice by using Staphylococcus aureus and Streptococcus pyogenes
- 2005
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Ingår i: Antimicrobial Agents and Chemotherapy. - 0066-4804 .- 1098-6596. ; 49:8, s. 3435-3441
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Tidskriftsartikel (övrigt vetenskapligt/konstnärligt)abstract
- A new animal model for the purpose of studying superficial infections is presented. In this model, an infection is established by disruption of the skin barrier by partial removal of the epidermal layer by tape stripping and subsequent application of the pathogens Staphylococcus aureus and Streptococcus pyogenes. The infection and the infection route are purely topical, in contrast to those used in previously described animal models in mice, such as the skin suture-wound model, where the infection is introduced into the deeper layers of the skin. Thus, the present model is considered more biologically relevant for the study of superficial skin infections in mice and humans. Established topical antibiotic treatments are shown to be effective. The procedures involved in the model are simple, a feature that increases throughput and reproducibility. This new model should be applicable to the evaluation of novel antimicrobial treatments of superficial infections caused by S. aureus and S. pyogenes.
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| 3. |
- Kugelberg, Elisabeth
(författare)
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Mechanisms of adaptive mutations in bacteria
- 2005
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Bacteria have the ability to adapt to various challenging environments. The rate, extent and consequences of bacterial adaptation depend on both microbial and environmental factors. This thesis analyses some of the mechanisms bacteria can employ to adapt to novel environments such as the presence of antibiotics, during infection of a host, and when exposed to growth-limiting conditions. Bacterial adaptation to antibiotics is conferred by mutations that usually modify essential cellular functions. In the absence of the drug, the adaptive mutations often confer a fitness cost measured as a decrease in growth rate and/or virulence. Bacteria can in many cases compensate for such fitness costs by acquiring second-site mutations. In Pseudomonas aeruginosa we showed that high levels of quinolone resistance are associated with high fitness costs. However, no-cost and compensatory mutations are common in strains resistant to low levels of quinolones. Decreased fitness, conferred by single resistance mutations in gyrA, was associated with decreased DNA supercoiling. Fitness and supercoiling could be restored to wild-type level without loss of resistance. The supply of mutations might be limiting during adaptation to novel selections. We showed that the rate of adaptation of Salmonella enterica serovar Typhimurium to mice could be accelerated by increases in the mutation supply, mediated by increased mutation rate or population size. An increased mutation rate was however associated with accumulation of deleterious mutations that decreased fitness in secondary environments. Bacterial adaptation to limiting growth conditions was studied in a genetic system that employs a strain with a mutant lac allele on plasmid F'lac128. This strain can adapt to growth on lactose by amplification of the mutant lac allele followed by mutation to Lac+. To further investigate the mechanisms behind this adaptation we identified and compared duplication join points detected before and after selection for gene amplification. We showed that large pre-existing lac duplications, with long sequence homologies, are common in the unselected population. In contrast, after selection for growth on lactose, most duplications were smaller with short sequence homologies at the join points. This discrepancy can be explained by the inefficiency of large duplications to amplify and form Lac+ revertants compared to shorter amplification units. Unique short homology join points could be detected in the unselected population although they were rare. Some short homology duplications may arise from remodeling of large duplications to yield a short amplicon that can amplify more efficiently. A subset of Lac+ revertants was associated with mutation accumulation in unselected genes. We showed that the unselected mutations were only detected in cells where the error-prone polymerase DinB was co-amplified with lac. Thus, the associated mutagenesis is a side effect when dinB and lac are within the same amplified unit. Taken together, these results further confirm that Lac+ revertants do not arise from a stress-induced hypermutable state as has been suggested. Instead Lac+ revertants arise by standard genetic events and stress functions only as an agent of natural selection, favoring growth of cells with a lac amplification.
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| 4. |
- Kugelberg, Elisabeth, et al.
(författare)
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Multiple pathways of selected gene amplification during adaptive mutation
- 2006
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Ingår i: Proceedings of the National Academy of Sciences of the United States of America. - : Proceedings of the National Academy of Sciences. - 0027-8424 .- 1091-6490. ; 103:46, s. 17319-17324
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Tidskriftsartikel (refereegranskat)abstract
- In a phenomenon referred to as "adaptive mutation," a population of bacterial cells with a mutation in the lac operon (lac-) accumulates Lac(+) revertants during prolonged exposure to selective growth conditions (lactose). Evidence was provided that selective conditions do not increase the mutation rate but instead favor the growth of rare cells with a duplication of the leaky lac allele. A further increase in copy number (amplification) improves growth and increases the likelihood of a sequence change by adding more mutational targets to the clone (cells and lac copies per cell). These duplications and amplifications are described here. Before selection, cells with large (134-kb) lac duplications and long junction sequences (> 1 kb) were common (0.2%). The same large repeats were found after selection in cells with a low-copy-number lac amplification. Surprisingly, smaller repeats (average, 34 kb) were found in high-copy-number amplifications. The small-repeat duplications form when deletions modify a preexisting large-repeat duplication. The shorter repeat size allowed higher lac amplification and better growth on lactose. Thus, selection favors a succession of gene-amplification types that make sequence changes more probable by adding targets. These findings are relevant to genetic adaptation in any biological systems in which fitness can be increased by adding gene copies (e.g., cancer and bacterial drug resistance).
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| 5. |
- Kugelberg, Elisabeth, et al.
(författare)
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Reduction of the fitness burden of quinolone resistance in Pseudomonas aeruginosa
- 2005
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Ingår i: Journal of Antimicrobial Chemotherapy. - : Oxford University Press (OUP). - 0305-7453 .- 1460-2091. ; 55:1, s. 22-30
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Tidskriftsartikel (refereegranskat)abstract
- Objectives: Quinolone resistance in the opportunistic pathogen Pseudomonas aeruginosa is commonly caused by mutations that alter the target molecules DNAgyrase/topoisomerase IV, or cause activation of various efflux systems.We have analysed the effect of quinolone resistance caused by DNA gyrase/topoisomerase IV mutations on bacterial fitness. Methods: Norfloxacin-resistant mutants were isolated and by DNA sequencing the mutations conferring resistance were identified. Mutant fitnesswas determined by measuring growth rates in vitro. Mutants with reducedgrowth rates were serially passaged to obtain growth-compensatedmutants. The level of DNA supercoiling was determined by isolatingplasmid DNA from the susceptible, resistant and compensated mutants andcomparing the topoisomer distribution patterns by gel electrophoresis inthe presence of chloroquine. Results: Low-level resistance (4-48 mg/L) was caused by single mutations in gyrA or gyrB. Among these strains, three out of eight mutants showed lower fitness,whereas high-level resistant (>256 mg/L) mutants with doublemutations in gyrA and parC, parE, nfxB or unknown genes all showed areduced fitness. Slow-growing resistantmutants with a gyrA mutation had decreased DNA supercoiling. Afterserial passage in laboratory medium, mutant fitnesswas increased by compensatory mutation(s) that restored supercoiling tonormal levels. The compensatory mutation(s) was not located in any ofthe genes (gyrAB, topA, parCE, hupB, fis, hupN, himAD or PA5348) thatwere expected to affect supercoiling. Conclusions: Our results show that 'no cost' and compensatory mutations are common in quinolone-resistant P. aeruginosa.
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| 6. |
- Kugelberg, Elisabeth, et al.
(författare)
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The Tandem Inversion Duplication in Salmonella enterica : Selection Drives Unstable Precursors to Final Mutation Types
- 2010
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Ingår i: Genetics. - : Oxford University Press (OUP). - 0016-6731 .- 1943-2631. ; 185:1, s. 65-80
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Tidskriftsartikel (refereegranskat)abstract
- During growth under selection, mutant types appear that are rare in unselected populations. Stress-induced mechanisms may cause these structures or selection may favor a series of standard events that modify common preexisting structures. One such mutation is the short junction (SJ) duplication with long repeats separated by short sequence elements: AB*(CD)*(CD)*E (* = a few bases). Another mutation type, described here, is the tandem inversion duplication (TID), where two copies of a parent sequence flank an inverse-order segment: AB(CD)(E'D'C'B')(CD) E. Both duplication types can amplify by unequal exchanges between direct repeats (CD), and both are rare in unselected cultures but common after prolonged selection for amplification. The observed TID junctions are asymmetric (aTIDs) and may arise from a symmetrical precursor (sTID)-ABCDE(E'D'C'B'A')ABCDE-when sequential deletions remove each palindromic junction. Alternatively, one deletion can remove both sTID junctions to generate an SJ duplication. It is proposed that sTID structures form frequently under all growth conditions, but are usually lost due to their instability and fitness cost. Selection for increased copy number helps retain the sTID and favors deletions that remodel junctions, improve fitness, and allow higher amplification. Growth improves with each step in formation of an SJ or aTID amplification, allowing selection to favor completion of the mutation process.
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| 7. |
- Kugelberg, Susanna, et al.
(författare)
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Public health nutrition workforce development in seven European countries : constraining and enabling factors
- 2012
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Ingår i: Public Health Nutrition. - Cambridge, United Kingdom : Cambridge University Press. - 1368-9800 .- 1475-2727. ; 15:11, s. 1989-1998
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Tidskriftsartikel (refereegranskat)abstract
- Objectives: Little is known about current public health nutrition workforce development in Europe. The present study aimed to understand constraining and enabling factors to workforce development in seven European countries.Design: A qualitative study comprised of semi-structured face-to-face interviews was conducted and content analysis was used to analyse the transcribed interview data.Setting: The study was carried out in Finland, Iceland, Ireland, Slovenia, Spain, Sweden and the UK.Subjects: Sixty key informants participated in the study.Results: There are constraining and enabling factors for public health nutrition workforce development. The main constraining factors relate to the lack of a supportive policy environment, fragmented organizational structures and a workforce that is not cohesive enough to implement public health nutrition strategic initiatives. Enabling factors were identified as the presence of skilled and dedicated individuals who assume roles as leaders and change agents.Conclusions: There is a need to strengthen coordination between policy and implementation of programmes which may operate across the national to local spectrum. Public health organizations are advised to further define aims and objectives relevant to public health nutrition. Leaders and agents of change will play important roles in fostering intersectorial partnerships, advocating for policy change, establishing professional competencies and developing education and training programmes.
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| 8. |
- Nilsson, Annika, et al.
(författare)
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Experimental adaptation of Salmonella typhimurium to mice
- 2004
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Ingår i: Genetics. - : Oxford University Press (OUP). - 0016-6731 .- 1943-2631. ; 168, s. 1119-1130
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Tidskriftsartikel (refereegranskat)abstract
- Experimental evolution is a powerful approach to study the dynamics and mechanisms of bacterial niche specialization. By serial passage in mice, we evolved 18 independent lineages of Salmonella typhimurium LT2 and examined the rate and extent of adaptation to a mainly reticuloendothelial host environment. Bacterial mutation rates and population sizes were varied by using wild-type and DNA repair-defective mutator (mutS) strains with normal and high mutation rates, respectively, and by varying the number of bacteria intraperitoneally injected into mice. After <200 generations of adaptation all lineages showed an increased fitness as measured by a faster growth rate in mice (selection coefficients 0.11–0.58). Using a generally applicable mathematical model we calculated the adaptive mutation rate for the wild-type bacterium to be >10−6/cell/generation, suggesting that the majority of adaptive mutations are not simple point mutations. For the mutator lineages, adaptation to mice was associated with a loss of fitness in secondary environments as seen by a reduced metabolic capability. During adaptation there was no indication that a high mutation rate was counterselected. These data show that S. typhimurium can rapidly and extensively increase its fitness in mice but this niche specialization is, at least in mutators, associated with a cost.
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| 9. |
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