| 1. |
- Arwidsson, Ola, et al.
(author)
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Evidence against reciprocal recombination as the basis for tuf gene conversion in Salmonella enterica serovar Typhimurium
- 2004
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In: Journal of Molecular Biology. - : Elsevier BV. - 0022-2836 .- 1089-8638. ; 338:3, s. 463-467
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Journal article (peer-reviewed)abstract
- The duplicate tuf genes on the Salmonella enterica serovar Typhimurium chromosome co-evolve by a RecA-, RecB-dependent gene conversion mechanism. Gene conversion is defined as a non-reciprocal transfer of genetic information. However, in a replicating bacterial chromosome there is a possibility that a reciprocal genetic exchange between different tuf genes sitting on sister chromosomes could result in "apparent" gene conversion. We asked whether the major mechanism of tuf gene conversion was classical or apparent. We devised a genetic selection that allowed us to isolate and examine both expected products from a reciprocal recombination event between the tuf genes. Using this selection we tested within individual cultures for a correlation in the frequency of jackpots as expected if recombination were reciprocal. We found no correlation, either in the frequency of each type of recombinant product, or in the DNA sequences of the products resulting from each recombination event. We conclude that the evidence argues in favor of a non-reciprocal gene conversion mechanism as the basis for tuf gene co-evolution.
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| 2. |
- Björkman, J, et al.
(author)
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Effects of environment on compensatory mutations to ameliorate costs of antibiotic resistance
- 2000
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In: Science. - : AMER ASSOC ADVANCEMENT SCIENCE. - 0036-8075 .- 1095-9203. ; 287:5457, s. 1479-1482
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Journal article (peer-reviewed)abstract
- Most types of antibiotic resistance impose a biological cost on bacterial fitness. These costs can be compensated, usually without loss of resistance, by second-site mutations during the evolution of the resistant bacteria in an experimental host or in a laboratory medium. Different fitness-compensating mutations were selected depending on whether the bacteria evolved through serial passage in mice or in a laboratory medium. This difference in mutation spectra was caused by either a growth condition-specific formation or selection of the compensated mutants. These results suggest that bacterial evolution to reduce the costs of antibiotic resistance can take different trajectories within and outside a host.
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| 3. |
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| 4. |
- Hughes, Diarmaid, 1956-
(author)
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Co-evolution of the tuf genes links gene conversion with the generation of chromosomal inversions
- 2000
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In: Journal of Molecular Biology. - : ACADEMIC PRESS LTD. - 0022-2836 .- 1089-8638. ; 297:2, s. 355-364
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Journal article (peer-reviewed)abstract
- The tufA and tufB genes in Salmonella typhimurium co-evolve by recombination and exchange of genetic material. A model is presented which predicts that co-evolution is achieved by gene conversions and chromosomal inversions. Analysis of recombinants reveals that conversion and inversion each occur with similar rates and each depends on RecBCD activity. The model predicts sequence structures for different classes of post-recombination tuf genes. Sequence analysis reveals the presence of each of these structures and classes, with a predicted bias in the absence of mismatch repair. An implication of these data is that co-evolution of gene families can be linked with the generation of chromosomal rearrangements.
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| 5. |
- Hughes, Diarmaid, 1956-
(author)
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Evaluating genome dynamics: the constraints on rearrangements within bacterial genomes
- 2000
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In: Genome Biology. - : Springer Science and Business Media LLC. - 1465-6906 .- 1474-760X. ; 1:6, s. 0006.1-0006.8
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Research review (other academic/artistic)abstract
- Inversions and translocations distinguish the genomes of closely related bacterial species, but most of these rearrangements preserve the relationship between the rearranged fragments and the axis of chromosome replication. Within species, such rearrangements are found less frequently, except in the case of clinical isolates of human pathogens, where rearrangements are very frequent.
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| 6. |
- Hughes, Diarmaid, 1956-, et al.
(author)
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Target alterations mediating antibiotic resistance
- 2001
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In: Antibiotic Development and Resistance. - : Taylor and Francis Publishers, London and New York. - 0415272173 ; , s. 23-36
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Book chapter (other academic/artistic)
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| 7. |
- Komp Lindgren, Patricia, et al.
(author)
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Mutation Rate and Evolution of Fluoroquinolone Resistance in Escherichia coli Isolates from Patients with Urinary tract infections
- 2003
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In: Antimicrobial Agents and Chemotherapy. - 0066-4804 .- 1098-6596. ; 47:10, s. 3222-3232
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Journal article (peer-reviewed)abstract
- Escherichia coli strains from patients with uncomplicated urinarytract infections were examined by DNA sequencing for fluoroquinoloneresistance-associated mutations in six genes: gyrA, gyrB, parC,parE, marOR, and acrR. The 54 strains analyzed had a susceptibilityrange distributed across 15 dilutions of the fluoroquinoloneMICs. There was a correlation between the fluoroquinolone MICand the number of resistance mutations that a strain carried,with resistant strains having mutations in two to five of thesegenes. Most resistant strains carried two mutations in gyrAand one mutation in parC. In addition, many resistant strainshad mutations in parE, marOR, and/or acrR. No (resistance) mutationwas found in gyrB. Thus, the evolution of fluoroquinolone resistanceinvolves the accumulation of multiple mutations in several genes.The spontaneous mutation rate in these clinical strains variedby 2 orders of magnitude. A high mutation rate correlated stronglywith a clinical resistance phenotype. This correlation suggeststhat an increased general mutation rate may play a significantrole in the development of high-level resistance to fluoroquinolonesby increasing the rate of accumulation of rare new mutations.
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| 8. |
- Laurberg, M, et al.
(author)
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Structure of a mutant EF-G reveals domain III and possibly the fusidic acid binding site
- 2000
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In: Journal of Molecular Biology. - : Elsevier BV. - 0022-2836 .- 1089-8638. ; 303:4, s. 593-603
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Journal article (peer-reviewed)abstract
- The crystal structure of Thermus thermophilus elongation factor G (EF-G) carrying the point mutation His573Ala was determined at a resolution of 2.8 Å. The mutant has a more closed structure than that previouslyreported for wild-type EF-G. This is obtained by a 10° rigid rotation of domains III, IV and V with regardto domains I and II. This rotation results in a displacement of the tipof domain IV by approximately 9 Å. The structure of domain III is nowfully visible and reveals the double split β-α-β motif also observed for EF-G domain V and for several ribosomal proteins. A large number of fusidic acid resistant mutations found in domain III have now been possible tolocate. Possible locations for the effector loop and a possible bindingsite for fusidic acid are discussed in relation to some of the fusidic acid resistant mutations.
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| 9. |
- Macvanin, Mirjana, et al.
(author)
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Fusidic acid-resistant EF-G perturbs the accumulation of ppGpp
- 2000
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In: Molecular Microbiology. - : Wiley. - 1365-2958 .- 0950-382X. ; 37:1, s. 98-107
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Journal article (peer-reviewed)abstract
- Reductions in growth rate caused by fusidic acid-resistant EF-G mutants in Salmonella typhimurium correlate strongly with increased mean cell size. This is unusual because growth rate and cell size normally correlate positively. The global transcription regulator molecule ppGpp has a role in co-ordinating growth rate and division, and its basal level normally correlates inversely with cell size at division. We show that fusidic acid-resistant EF-G mutants have perturbed ppGpp basal levels during steady-state growth and perturbed induced levels during starvation. One mutation, fusA1, associated with the slowest growth rate and largest cell size, causes a reduction in the basal level of ppGpp to one-third of that found in the wild-type strain. Other fusA mutants with intermediate or wild-type growth rates and cell sizes have either normal or increased basal levels of ppGpp. There is an inverse relationship between the basal level of ppGpp in vivo and the degree to which translation dependent on mutant EF-G is inhibited by ppGpp in vitro. This enhanced interaction between mutant EF-G and ppGpp correlates with an increased KM for GTP. Our results suggest that mutant EF-G modulates the production of ppGpp by the RelA (PSI) pathway. In conclusion, fusidic acid-resistant EF-G mutations alter the level of ppGpp and break the normal relationship between growth rate and cell size at division. It would not be surprising if other phenotypes associated with these mutants, such as loss of virulence, were also related to perturbations in ppGpp levels effected through altered transcription patterns.
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| 10. |
- Macvanin, Mirjana, et al.
(author)
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Fusidic acid-resistant mutants of Salmonella enterica serovar typhimurium have low levels of heme and a reduced rate of respiration and are sensitive to oxidative stress
- 2004
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In: Antimicrobial Agents and Chemotherapy. - 0066-4804 .- 1098-6596. ; 48:10, s. 3877-3883
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Journal article (peer-reviewed)abstract
- Mutations in the translation elongation factor G (EF-G) make Salmonella enterica serovar Typhimurium resistant to the antibiotic fusidic acid. Fusr mutants are hypersensitive to oxidative stress and rapidly lose viability in the presence of hydrogen peroxide. We show that this phenotype is associated with reduced activity of two catalase enzymes, HPI (a bifunctional catalase-hydroperoxidase) and HPII (a monofunctional catalase). These catalases require the iron-binding cofactor heme for their activity. Fusr mutants have a reduced rate of transcription of hemA, a gene whose product catalyzes the first committed step in heme biosynthesis. Hypersensitivity of Fusr mutants to hydrogen peroxide is abolished by the presence of -aminolevulinic acid, the precursor of heme synthesis, in the growth media and by the addition of glutamate or glutamine, amino acids required for the first step in heme biosynthesis. Fluorescence measurements show that the level of heme in a Fusr mutant is significantly lower than it is in the wild type. Heme is also an essential cofactor of cytochromes in the electron transport chain of respiration. We found that the rate of respiration is reduced significantly in Fusr mutants. Sequestration of divalent iron in the growth media decreases the sensitivity of Fusr mutants to oxidative stress. Taken together, these results suggest that Fusr mutants are hypersensitive to oxidative stress because their low levels of heme reduce both catalase activity and respiration capacity. The sensitivity of Fusr mutants to oxidative stress could be associated with loss of viability due to iron-mediated DNA damage in the presence of hydrogen peroxide. We argue that understanding the specific nature of antibiotic resistance fitness costs in different environments may be a generally useful approach in identifying physiological processes that could serve as novel targets for antimicrobial agents.
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| 11. |
- Macvanin, Mirjana, et al.
(author)
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Fusidic acid-resistant mutants of Salmonella enterica serovar Typhimurium with low fitness in vivo are defective in RpoS induction
- 2003
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In: Antimicrobial Agents and Chemotherapy. - 0066-4804 .- 1098-6596. ; 47:12, s. 3743-3749
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Journal article (peer-reviewed)abstract
- Mutants of Salmonella enterica serovar Typhimurium resistant to fusidic acid (Fusr) have mutations in fusA, the gene encoding translation elongation factor G (EF-G). Most Fusr mutants have reduced fitness in vitro and in vivo, in part explained by mutant EF-G slowing the rate of protein synthesis and growth. However, some Fusr mutants with normal rates of protein synthesis still suffer from reduced fitness in vivo. As shown here, Fusr mutants could be similarly ranked in their relative fitness in mouse infection models, in a macrophage infection model, in their relative hypersensitivity to hydrogen peroxide in vivo and in vitro, and in the amount of RpoS production induced upon entry into the stationary phase. We identify a reduced ability to induce production of RpoS (sigmas) as a defect associated with Fusr strains. Because RpoS is a regulator of the general stress response, and an important virulence factor in Salmonella, an inability to produce RpoS in appropriate amounts can explain the low fitness of Fusr strains in vivo. The unfit Fusr mutants also produce reduced levels of the regulatory molecule ppGpp in response to starvation. Because ppGpp is a positive regulator of RpoS production, we suggest that a possible cause of the reduced levels of RpoS is the reduction in ppGpp production associated with mutant EF-G. The low fitness of Fusr mutants in vivo suggests that drugs that can alter the levels of global regulators of gene expression deserve attention as potential antimicrobial agents.
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| 12. |
- Macvanin, Mirjana, et al.
(author)
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The physiological cost of antibiotic resistance
- 2003
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In: Recent research developments in microbiology. - Trivandrum, India : Research Signpost. ; 7, s. 607-629
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Research review (pop. science, debate, etc.)
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| 13. |
- Nagaev, Ivan, et al.
(author)
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Biological cost and compensatory evolution in fusidic acid-resistant Staphylococcus aureus
- 2001
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In: Molecular Microbiology. - : BLACKWELL SCIENCE LTD. - 0950-382X .- 1365-2958. ; 40:2, s. 433-439
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Journal article (peer-reviewed)abstract
- Fusidic acid resistance resulting from mutations in elongation factor G (EF-G) of Staphylococcus aureus is associated with fitness costs during growth in vivo and in vitro. In both environments, these costs can be partly or fully compensated by the acquisition of secondary intragenic mutations. Among clinical isolates of S. aureus, fusidic acid-resistant strains have been identified that carry multiple mutations in EF-G at positions similar to those shown experimentally to cause resistance and fitness compensation. This observation suggests that fitness-compensatory mutations may be an important aspect of the evolution of antibiotic resistance in the clinical environment, and may contribute to a stabilization of the resistant bacteria present in a bacterial population.
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