Publications (39)140.71 Total impact
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Article: Evolution and mechanisms for spread of antimicrobial resistance.
Acta veterinaria Scandinavica. Supplementum 02/2000; 93:23-7; discussion 28-36. -
Article: An integron cassette carrying dfr1 with 90-bp repeat sequences located on the chromosome of trimethoprim-resistant isolates of Campylobacter jejuni.
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ABSTRACT: The frequent occurrence of high-level trimethoprim resistance in clinical isolates of Campylobacter jejuni was shown to be related to the acquisition of foreign resistance genes (dfrl or dfr9 or both) coding for resistant variants of the enzyme dihydrofolate reductase, the target of trimethoprim. The dfr1 gene detected on the chromosome of 40 different clinical strains of C. jejuni was studied further regarding structure and genetic organization. Most of the dfr1 genes were found as integron cassettes inserted in the chromosome. In 36% of the examined isolated, the dfr1 gene showed identity to that previously characterized in trimethoprim-resistant Escherichia coli. In 40% of the cases, however, a variant of the dfr1 gene containing a 90-bp direct repeat was detected, and in 5% of the isolates, the repeat-containing dfr1 variant was found to occur in the form of two cassettes in tandem in an integron context. The existence of the 90-bp repeat within the coding sequence of the dfr1gene was found to play a role in the adaptation of C. jejuni to ambient concentrations of trimethoprim.Microbial Drug Resistance 02/2000; 6(2):91-8. · 2.15 Impact Factor -
Article: Sulfonamide resistance in clinical isolates of Campylobacter jejuni: mutational changes in the chromosomal dihydropteroate synthase.
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ABSTRACT: The characterization of the genetic basis of sulfonamide resistance in Campylobacter jejuni was attempted. The resistance determinant from a sulfonamide-resistant strain of C. jejuni was cloned and was found to show 42% identity with the folP gene (which codes for dihydropteroate synthase, the target of sulfonamides) of the related bacterium Helicobacter pylori. The sequences of the areas surrounding the folP gene in C. jejuni showed similarity to those of the areas surrounding the corresponding gene in H. pylori. The folP gene of C. jejuni, which mediates the resistance, was observed to show particular features when it was compared to other known folP genes. One of these features is the presence of two pairs of direct repeats (15 and 27 bp) within the coding sequence of the gene. Comparison of the C. jejuni folP genes that mediate susceptibility and resistance revealed the occurrence of mutations that changed four amino acid residues. Resistance of C. jejuni to sulfonamides could be associated with one or several of these four mutational substitutions, which all occurred in the five different resistant isolates studied. The codon for one of these changed amino acids was found to be located in the second direct repeat within the coding sequence of the gene. The change made the repeat perfect. The transformation of both the resistance and the susceptibility variants of the gene into an Escherichia coli folP knockout mutant was found to complement the dihydropteroate synthase deficiency, confirming that the characterized sulfonamide resistance determinant codes for the C. jejuni dihydropteroate synthase enzyme. Kinetic measurements established different affinities of sulfonamide for the dihydropteroate synthase enzyme isolated from the resistant and susceptible strains. In conclusion, sulfonamide resistance in C. jejuni was shown to be associated with mutational changes in the chromosomally located gene for dihydropteroate synthase, the target of sulfonamides.Antimicrobial Agents and Chemotherapy 10/1999; 43(9):2156-60. · 4.84 Impact Factor -
Article: [A new antibacterial agent can stop resistance development. Expectations are connected to linezolid, an oxazolidinone with a new pharmacological action].
Lakartidningen 10/1999; 96(37):3866-7. -
Article: Molecular epidemiology of Plasmodium falciparum antifolate resistance in Vietnam: genotyping for resistance variants of dihydropteroate synthase and dihydrofolate reductase.
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ABSTRACT: Using PCR techniques, we analysed the dihydropteroate synthase (DHPS) mutations associated with sulphonamide resistance and the dihydrofolate reductase (DHFR) mutations associated with resistance to pyrimethamine and cycloguanil in samples from Plasmodium falciparum-infected Vietnamese patients. Of the 40 samples analysed, 39 had DHFR mutations associated with high level resistance to pyrimethamine, whereas only three had mutations at position 164, which is linked to cross resistance to both DHFR inhibitors. The DHPS, 437Gly variant associated with very mild resistance to sulphadoxine was found in 38 out of the 40 samples. Of seven samples resistant to Fansidar in vivo, only two were fully explained by the currently documented DHPS mutations. The treatment failure could be due to a high level of pyrimethamine resistance caused by the detected mutations. Most patients, however, were cured with a single dose of Fansidar in spite of the high number of resistance mutations found.International Journal of Antimicrobial Agents 09/1999; 12(3):203-11. · 4.13 Impact Factor -
Article: High-level resistance to trimethoprim in clinical isolates of Campylobacter jejuni by acquisition of foreign genes (dfr1 and dfr9) expressing drug-insensitive dihydrofolate reductases.
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ABSTRACT: The pathogenic bacterium Campylobacter jejuni has been regarded as endogenously resistant to trimethoprim. The genetic basis of this resistance was characterized in two collections of clinical isolates of C. jejuni obtained from two different parts of Sweden. The majority of these isolates were found to carry foreign dfr genes coding for resistant variants of the dihydrofolate reductase enzyme, the target of trimethoprim. The resistance genes, found on the chromosome, were dfr1 and dfr9. In about 10% of the strains, the dfr1 and dfr9 genes occurred simultaneously. About 10% of the examined isolates were found to be negative for these dfr genes and showed a markedly lower trimethoprim resistance level than the other isolates. The dfr9 and dfr1 genes were located in the context of remnants of a transposon and an integron, respectively. Two different surroundings for the dfr9 gene were characterized. One was identical to the right-hand end of the transposon Tn5393, and in the other, the dfr9 gene was flanked by only a few nucleotides of a Tn5393 sequence. The insertion of the dfr9 gene into the C. jejuni chromosome could have been mediated by Tn5393. The frequent occurrence of high-level trimethoprim resistance in clinical isolates of C. jejuni could be related to the heavy exposure of food animals to antibacterial drugs, which could lead to the acquisition of foreign resistance genes in naturally transformable strains of C. jejuni.Antimicrobial Agents and Chemotherapy 01/1999; 42(12):3059-64. · 4.84 Impact Factor -
Article: Sulfonamide resistance in Streptococcus pyogenes is associated with differences in the amino acid sequence of its chromosomal dihydropteroate synthase.
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ABSTRACT: Sulfonamide resistance in recent isolates of Streptococcus pyogenes was found to be associated with alterations of the chromosomally encoded dihydropteroate synthase (DHPS). There were 111 different nucleotides (13.8%) in the genes found in susceptible and resistant isolates, respectively, resulting in 30 amino acid changes (11.3%). These substantial changes suggested the possibility of a foreign origin of the resistance gene, in parallel to what has already been found for sulfonamide resistance in Neisseria meningitidis. The gene encoding DHPS was linked to at least three other genes encoding enzymes of the folate pathway. These genes were in the order GTP cyclohydrolase, dihydropteroate synthase, dihydroneopterin aldolase, and hydroxymethyldihydropterin pyrophosphokinase. The nucleotide differences in genes from resistant and susceptible strains extended from the beginning of the GTP cyclohydrolase gene to the end of the gene encoding DHPS, an additional indication for gene transfer in the development of resistance. Kinetic measurements established different affinities for sulfathiazole for DHPS enzymes isolated from resistant and susceptible strains.Antimicrobial Agents and Chemotherapy 06/1998; 42(5):1062-7. · 4.84 Impact Factor -
Article: Macrolide resistance in Helicobacter pylori: mechanism and stability in strains from clarithromycin-treated patients.
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ABSTRACT: Helicobacter pylori strains from seven patients treated with clarithromycin were investigated for development, mechanism, and stability of resistance. Genetic relatedness between pre- and posttreatment isolates was shown by arbitrary primed PCR. Clarithromycin resistance was associated with A-to-G transitions at either position 2143 or 2144 or at both positions 2116 and 2142. In four cases, the mutations were homozygous. The Cla(r) phenotype was stable after 50 subcultivations in vitro. No erythromycin-modifying enzymes or rRNA methylases were found by biological assays, PCR and sequencing, or cloning methods.Antimicrobial Agents and Chemotherapy 12/1997; 41(11):2550-3. · 4.84 Impact Factor -
Article: Non-palindromic attl sites of integrons are capable of site-specific recombination with one another and with secondary targets.
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ABSTRACT: Genes borne on cassettes are mobile owing to site-specific recombination systems called integrons, which have created various combinations of antibiotic resistance genes in R-plasmids. In these processes, the palindromic site, attC (59-base element), at cassette junctions has been proposed as being essential. Excised and circularized cassettes have been found to integrate with preference for an attl site at one end of the conserved sequence in integrons. In this work, we give evidence that recombination is possible in the absence of the highly organized attC sites between the more simply organized attl sites. Furthermore, at a very low frequency representing the background in our recombination assay, we observed cross-overs between attl and secondary sites. To characterize recombination excluding the attC sites, we have used naturally occurring attl variants and constructed mutants. The cross-over point was identified between a guanine and a thymine in attl using point mutations. Progressive deletions showed the extent of attl and identified two important regions in the conserved sequence 5' of the cross-over point. A region 27-36 bp 5' of attl influenced recombination with attC sites only, whereas a sequence 9-14 bp 5' of the cross-over point in attl was important for recombination with both attl and attC. Recombination between attl and secondary sites could allow fusion of the conserved sequence encoding the integron site-specific recombinase to new sequences.Molecular Microbiology 12/1997; 26(3):441-53. · 5.01 Impact Factor -
Article: Plasmodium falciparum: mutation pattern in the dihydrofolate reductase-thymidylate synthase genes of Vietnamese isolates, a novel mutation, and coexistence of two clones in a Thai patient.
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ABSTRACT: Pyrimethamine and cycloguanil resistance of Plasmodium falciparum has been linked to mutations in the dihydrofolate reductase (dhfr) portion of the dhfr-ts gene. In this paper, the DNA sequence of the dhfr-ts gene of 50 isolates from Vietnam and 2 clones (T9/94 and T9/96) isolated from a malaria patient from Thailand have been analyzed. A comparison between these isolates and clones showed differential mutation patterns. Forty-eight isolates were found to consist of mutations associated with Pyr. A novel leucine mutation at position 140 was found in the isolate VP8 and in clone T9/94. The isolate VP8 and the clone T9/94 were found to also have the characteristic changes at positions 16 (Val) and 108 (Thr) that have been found in cycloguanil-resistant isolates. The isolate VP35 was shown to be resistant to both antifolates, while the clone T9/96 was found to be sensitive to both antifolates and to have a sequence identical to that of wild-type dhfr-ts. The two clones from a single patient showed the coexistence of resistant and sensitive clones in the absence of treatment by antifolates. Since cycloguanil resistance seems to be rare in Vietnam, cycloguanil alone or in combination with other antimalarial agents might be an alternative for treatment and prophylaxis, even in areas with high resistance to pyrimethamine.Experimental Parasitology 11/1996; 84(1):56-64. · 2.12 Impact Factor -
Article: Sulfonamide resistance in Neisseria meningitidis as defined by site-directed mutagenesis could have its origin in other species.
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ABSTRACT: Sulfonamide resistance in Neisseria meningitidis is mediated by altered forms of the chromosomal gene for the drug target enzyme dihydropteroate synthase. Sulfonamides have been used for decades both for prophylaxis and the treatment of meningococcal disease, and resistance is common. Two types of resistance determinants have been identified, and regions important for drug insusceptibility to the corresponding enzyme have been defined by site-directed mutagenesis. Both types of resistance traits have spread among strains of N. meningitidis of different serogroups and serotypes, and the large differences at the nucleotide level in a comparison of the resistance genes with the dhps genes of susceptible meningococci indicate the origin of one or maybe both types in other Neisseria species. One sulfonamide-sensitive strain of N. meningitidis was found to have a mosaic dhps gene with a central part identical to the corresponding part of a gonococcal strain. This observation supports the idea of an interspecies transfer of genetic material in Neisseria species as a mechanism for the development of chromosomally mediated resistance.Journal of Bacteriology 09/1995; 177(16):4669-75. · 3.83 Impact Factor -
Article: PCR amplicon restriction endonuclease analysis of the chromosomal dhps gene of Neisseria meningitidis: a method for studying spread of the disease-causing strain in contacts of patients with meningococcal disease.
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ABSTRACT: We tested two sets of primers derived from the dhps gene of Neisseria meningitidis for the amplification of meningococcal DNA by PCR. Both the NM1-NM6 primers and the NM3-NM6 primers amplified dhps DNA from all of the meningococci included in the study, resulting, in most cases, in amplicons of 0.70 and 0.23 kb, respectively. Also, dhps DNAs of N. gonorrhoeae and some commensals were amplified but Haemophilus influenzae, Streptococcus pneumoniae, and Escherichia coli DNAs were not. By PCR amplicon restriction endonuclease analysis (AREA) of the larger amplicon, we could differentiate between individual strains of N. meningitidis. Following two cases of meningococcal disease, we used PCR AREA to identify healthy contacts carrying the disease-causing strain. We conclude that PCR AREA is a useful method for meningococcal strain differentiation and that it has potential as a method for studying the spread of a disease-causing strain in an affected population. The method is quicker and easier to perform and interpret than chromosomal DNA fingerprinting.Journal of Clinical Microbiology 06/1995; 33(5):1174-9. · 4.15 Impact Factor -
Article: Trimethoprim and sulfonamide resistance.
Antimicrobial Agents and Chemotherapy 03/1995; 39(2):279-89. · 4.84 Impact Factor -
Article: A new dhfrVIII trimethoprim-resistance gene, flanked by IS26, whose product is remote from other dihydrofolate reductases in parsimony analysis.
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ABSTRACT: A new plasmid-borne gene, dhfrVIII, encoding high-level trimethoprim resistance (TpR) was found in an intestinal Escherichia coli. It seems to be a widely occurring mediator of TpR. Among 973 examined TpR E. coli, the new resistance gene was found in 13 (1.3%) isolates from Sweden, Finland and Nigeria. The new gene was sequenced and found to code for a dihydrofolate reductase (DHFR) of 169 amino acids (M(r) 19005). The dhfrVIII gene on the studied plasmid pLMO226 was observed to be flanked by IS26 elements. The dhfrVIII gene and a 3' unidentified open reading frame (ORF) seem to be borne on a compound transposon with IS26 at its ends, since the configuration of two IS26 flanking dhfrVIII and the unidentified ORF was conserved among the isolates that were probe-positive for the gene. Phylogeny parsimony analysis showed the dhfrVIII-encoded enzyme to be only remotely related to other known plasmid-mediated, drug-resistant DHFR. Only a few of the latter form well-supported monophyletic groups.Gene 03/1995; 154(1):7-14. · 2.34 Impact Factor -
Article: Transposon Tn5090 of plasmid R751, which carries an integron, is related to Tn7, Mu, and the retroelements.
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ABSTRACT: Integrons confer on bacterial plasmids a capability of taking up antibiotic resistance genes by integrase-mediated recombination. We show here that integrons are situated on genetic elements flanked by 25-bp inverted repeats. The element carrying the integron of R751 has three segments conserved with similar elements in Tn21 and Tn5086. Several characteristics suggest that this element is a transposon, which we call Tn5090. Tn5090 was shown to contain an operon with three open reading frames, of which two, tniA and tniB, were predicted by amino acid similarity to code for transposition proteins. The product of tniA (559 amino acids) is a probable transposase with 25% amino acid sequence identity to TnsB from Tn7. Both of these polypeptides contain the D,D(35)E motif characteristic of a protein family made up of the retroviral and retrotransposon IN proteins and some bacterial transposases, such as those of Tn552 and of a range of insertion sequences. Like the transposase genes in Tn552, Mu, and Tn7, the tniA gene was followed by a gene, tniB, for a probable ATP-binding protein. The ends of Tn5090, like those of most other elements producing D,D(35)E proteins, begin by 5'-TG and also contains a complex structure with four 19-bp repeats at the left end and three at the right end. Similarly organized repeats have been observed earlier at the termini of both Tn7 and phage Mu, where they bind their respective transposases and have a role in holoenzyme assembly. Another open reading frame observed in Tn5090, tniC, codes for a recombinase of the invertase/resolvase family, suggesting a replicative transposition mechanism. The data presented here suggest that Tn5090, Tn7, Tn552, and Mu form a subfamily of bacterial transposons which in parallel to many insertion sequences are related to the retroelements.Journal of Bacteriology 07/1994; 176(11):3257-68. · 3.83 Impact Factor -
Article: The 3' conserved segment of integrons contains a gene associated with multidrug resistance to antiseptics and disinfectants.
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ABSTRACT: Nucleotide sequence analysis of ORF1 from the integron on the broad-host-range plasmid R751 revealed that the first 94 of 110 codons of ORF1 from R751 are identical to ORF4, an open reading frame from the 3' conserved segment of other integrons found in gram-negative bacteria, after which point they diverged completely. The predicted products of both ORF1 and ORF4 share homology with the multidrug exporter QacC. Phenotypic analysis revealed that ORF1 specifies a resistance profile to antiseptics and disinfectants almost identical to that of qacC, whereas ORF4 specifies much lower levels of resistance to these compounds. ORF4, whose product lacks the C-terminal 16 amino acids of the ORF1 protein, may have evolved by the interruption of ORF1 from the insertion of a DNA segment carrying a sulI sulfonamide resistance determinant. Hence, ORF1 was designated qacE, and its partially functional deletion derivative, ORF4, was designated qacE delta 1. Fluorimetric experiments indicated that the mechanism of resistance mediated by QacE, the protein specified by qacE, is active export energized by proton motive force. Amino acid sequence comparisons revealed that QacE is related to a family of small multidrug export proteins with four transmembrane segments.Antimicrobial Agents and Chemotherapy 05/1993; 37(4):761-8. · 4.84 Impact Factor -
Article: Characterization of transposon Tn5086, carrying the site-specifically inserted gene dhfrVII mediating trimethoprim resistance.
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ABSTRACT: Two different enteric plasmids of widely separate origins were observed to carry a new 15.3-kb trimethoprim resistance transposon, Tn5086, also mediating resistance to mercuric ions and to a low level of sulfonamide. The trimethoprim resistance gene characterized from Tn5086 was found to be distinct from those found earlier and was designated type VII. Molecular analysis demonstrated that Tn5086 is closely related to Tn21. The internal part of Tn21 and Tn5086, the element referred to as the integron, was found to be different. First, the integron of Tn5086 contains a 0.62-kb cassette formed by the trimethoprim resistance gene dhfrVII and its immediate surroundings instead of the 0.86-kb aadA1 cassette of Tn21. Second, the integron of Tn5086 lacks a 4.2-kb segment 3' of sulI in Tn21. The dhfrVII gene commences with a UUG codon but was otherwise seen to be markedly related to the cassette genes dhfrI, dhfrV, and dhfrVI. The four related dihydrofolate reductases of 157 amino acids encoded by these genes contain a glutamate instead of the aspartic acid residue found at position 27 of the active center of the chromosomal enzyme from Escherichia coli.Journal of Bacteriology 04/1993; 175(6):1796-805. · 3.83 Impact Factor -
Article: Trimethoprim resistance arising in animal bacteria and transferring into human pathogens.
The Journal of Infectious Diseases 04/1993; 167(3):785-7. · 6.41 Impact Factor -
Article: Point mutations in the dihydropteroate synthase gene causing sulfonamide resistance.
Advances in experimental medicine and biology 02/1993; 338:555-8. · 1.09 Impact Factor -
Article: Spread of a newly found trimethoprim resistance gene, dhfrIX, among porcine isolates and human pathogens.
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ABSTRACT: A plasmid-borne gene mediating trimethoprim resistance, dhfrIX, newly found among porcine strains of Escherichia coli, was observed at a frequency of 11% among trimethoprim-resistant veterinary isolates. This rather high frequency of dhfrIX could be due to the extensive use of trimethoprim in veterinary practice in Sweden. After searching several hundred clinical isolates, one human E. coli strain was also found to harbor the dhfrIX gene. Thus, the dhfrIX gene seems to have spread from porcine bacteria to human pathogens. Furthermore, the occurrence of other genes coding for resistant dihydrofolate reductase enzymes (dhfrI, dhfrII, dhfrV, dhfrVII, and dhfrVIII) among the porcine isolates was investigated. In addition, association of dhfr genes with the integraselike open reading frames of transposons Tn7 and Tn21 was studied. In colony hybridization experiments, both dhfrI and dhfrII were found associated with these integrase genes. The most common combination was dhfrI and int-Tn7, indicating a high prevalence of Tn7.Antimicrobial Agents and Chemotherapy 01/1993; 36(12):2704-8. · 4.84 Impact Factor
Top co-authors
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Institutions
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1979–2000
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Uppsala University
- • Department of Pharmaceutical Biosciences
- • Department of Surgical Sciences
- • Faculty of Pharmacy
Uppsala, Uppsala, Sweden
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1995
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National Public Health Institute
Helsinki, Province of Southern Finland, Finland
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1992
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Lund University
- Department of Chemistry
Lund, Skane, Sweden
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