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P Zawadzki

Publications and source records attributed to P Zawadzki.

At least 19 recordsLinked to original sources
PubMed2007

Hepatitis C Virus p7 membrane protein quasispecies variability in chronically infected patients treated with interferon and ribavirin, with or without amantadine.

A clinical study was carried out to compare the response rate of two groups of non-responder (NR) hepatitis C virus (HCV) genotype 1 chronically infected patients treated with interferon and ribavirin, with or without amantadine. The viral load decreased more markedly in the group treated by tritherapy including amantadine, but the response rate at the end of treatment was not significantly different between bitherapy and tritherapy. As amantadine could have an antiviral effect on the ion channel activity of the p7 HCV protein, the p7 quasispecies was characterized by cloning and sequencing. Sequence data were analyzed to determine the pattern and significance of p7 genetic heterogeneity and a possible relationship with therapy. Subtype differences were confirmed between p7 HCV genotypes 1a and 1b, and quasispecies analysis showed a reduction of genetic diversity in subtype 1a, but not 1b, during tritherapy. However, the absence of changes at numerous positions, as well as the conservative changes at other positions, indicated the high conservation of the p7 structure. Residue His-17, proposed to interact with amantadine, was fully conserved in both subtypes 1a and 1b, independently of amantadine administration. In conclusion, although the analysis of the p7 sequences revealed a selective pressure during therapy, no specific residues appeared to be linked to the effect of amantadine on viral decline. These results suggest that the potential antiviral effect of amantadine might be non-specific and related to a reduction in endosomal acidification and therefore reduced viral entry of HCV via its pH-dependent pathway.

Adult↗
PubMed2006

Stability diagram of a few-electron triple dot.

Individual and coupled quantum dots containing one or two electrons have been realized and are regarded as components for future quantum information circuits. In this Letter we map out experimentally the stability diagram of the few-electron triple dot system, the electron configuration map as a function of the external tuning parameters, and reveal experimentally for the first time the existence of quadruple points, a signature of the three dots being in resonance. In the vicinity of these quadruple points we observe a duplication of charge transfer transitions related to charge and spin reconfigurations triggered by changes in the total electron occupation number. The experimental results are largely reproduced by equivalent circuit analysis and Hubbard models. Our results are relevant for future quantum mechanical engineering applications within both quantum information and quantum cellular automata architectures.

Journal Article↗
PubMed2003

Spin-blockade spectroscopy of a two-level artificial molecule.

Coulomb- and spin-blockade spectroscopy investigations have been performed on an electrostatically defined "artificial molecule" connected to spin polarized leads. The molecule is first effectively reduced to a two-level system by placing both constituent atoms at a specific location of the level spectrum. The spin sensitivity of the conductance enables us to identify the electronic spin states of the two-level molecule. We find in addition that the magnetic field induces variations in the tunnel coupling between the two atoms. The lateral nature of the device is evoked to explain this behavior.

Journal Article↗
PubMed2003

Oral cavity as a potential source of infections in recipients with diabetes mellitus.

Our previous observations showed alterations of oral cavity status among hemodialyzed patients and kidney allograft recipients as well as differences in the prevalence and composition of microorganisms occurring in the mouths of patients. In the present work, we analysed the results of oral cavity examinations, the identification of microorganisms, and the assessment of their importance to kidney allograft recipients or hemodialyzed patients with diabetes mellitus, in comparison with nondiabetic recipients, dialyzed patients, and control patients.

Adult↗
PubMed2000

Genetic diversity of the tet(M) gene in tetracycline-resistant clonal lineages of Streptococcus pneumoniae.

The aim of the present study was to examine the stability and evolution of tet(M)-mediated resistance to tetracyclines among members of different clonal lineages of Streptococcus pneumoniae. Thirty-two tetracycline-resistant isolates representing three national (Spanish serotype 14, Spanish serotype 15, and Polish serotype 23F) and one international (Spanish serotype 23F) multidrug-resistant epidemic clones were all found to be tet(M) positive and tet(O), tet(K), and tet(L) negative. These isolates all carried the integrase gene, int, which is associated with the Tn1545-Tn916 family of conjugative transposons. High-resolution restriction analysis of tet(M) products identified six alleles, tet(M)1 to tet(M)6: tet(M)1 to tet(M)3 and tet(M)5 in isolates of the Spanish serotype 14 clone, tet(M)4 in both the Spanish serotype 15 and 23F clones, and tet(M)6, the most divergent allele, in the Polish 23F clone. This indicates that tet(M) variation can occur at the inter- and intraclone levels in pneumococci. Two alleles of int were identified, with int1 being found in all isolates apart from members of the international Spanish 23F clone, which carried int2. Susceptibility to tetracycline, doxycycline, and minocycline was evaluated for all isolates with or without preincubation in the presence of subinhibitory concentrations of tetracyclines. Resistance to tetracyclines was found to be inducible in isolates of all clones; however, the strongest induction was observed in the Spanish serotype 15 and 23F clones carrying tet(M)4. Tetracycline was found to be the strongest inducer of resistance, and minocycline was found to be the weakest inducer of resistance.

Bacterial Proteins↗
PubMed2000

Barriers to genetic exchange between bacterial species: Streptococcus pneumoniae transformation.

Interspecies genetic exchange is an important evolutionary mechanism in bacteria. It allows rapid acquisition of novel functions by transmission of adaptive genes between related species. However, the frequency of homologous recombination between bacterial species decreases sharply with the extent of DNA sequence divergence between the donor and the recipient. In Bacillus and Escherichia, this sexual isolation has been shown to be an exponential function of sequence divergence. Here we demonstrate that sexual isolation in transformation between Streptococcus pneumoniae recipient strains and donor DNA from related strains and species follows the described exponential relationship. We show that the Hex mismatch repair system poses a significant barrier to recombination over the entire range of sequence divergence (0.6 to 27%) investigated. Although mismatch repair becomes partially saturated, it is responsible for 34% of the observed sexual isolation. This is greater than the role of mismatch repair in Bacillus but less than that in Escherichia. The remaining non-Hex-mediated barrier to recombination can be provided by a variety of mechanisms. We discuss the possible additional mechanisms of sexual isolation, in view of earlier findings from Bacillus, Escherichia, and Streptococcus.

Base Pair Mismatch↗
PubMed1997

Direct blotting electrophoresis for sequencing and genotyping hepatitis C virus.

Many methods have been used to differentiate the hepatitis C virus (HCV) genotypes based on, for example, type specific primers, probes and restriction fragment length polymorphism. However, determination of the nucleotide sequence remains the reference. Therefore, a simple non-radioactive cycle sequencing technique was developed for clinical tests. PCR-amplified products of the 5' non-coding region (from position -274 to -31) were sequenced using a 5' digoxygenin-labeled primer. After denaturation, the samples were loaded on a direct blotting electrophoresis system (GATC 1500). Sequencing products were blotted onto a nylon membrane during the electrophoresis. The DNA fragments were then UV-cross-linked, incubated with phosphatase-labeled anti-digoxygenin antibody and stained with a precipitating substrate. Reading the sequence of six samples were possible within 2 days. In 41 different samples, five different genotypes were found by sequence analysis from position -245 to -69, of which 17 were type 1a, 7 type 1b, 5 type 2a, 8 type 3a, 3 type 4 and 1 type 5. These results agreed with those obtained by reverse hybridization assay. Direct blotting electrophoresis offered a good non-radioactive method of performing clinical sequencing on a medium scale, with a minimum of investment.

Adult↗
PubMed1997

Comparison of hepatitis C virus serotyping and genotyping in French patients.

BACKGROUND: Hepatitis C virus (HCV) serotyping has been proposed as an alternative assay to determine the respective genotype as it is more rapid, simple and less expensive than polymerase chain reaction (PCR) based typing methods. OBJECTIVES: A serotyping assay was compared with a genotyping assay to determine the infecting hepatitis C virus type in chronically HCV infected patients eligible for interferon therapy. STUDY DESIGN: An enzyme immunoassay (HC01, Murex) was tested to identify HCV types 1, 2 and 3 specific antibodies in 134 PCR-positive sera from chronically infected patients which had been previously genotyped by a reverse hybridization assay (INNO-LiPA HCV I, Innogenetics). Respectively nine and seven sera were from HIV-seropositive and hemodialysis patients. Unreactive sera and those with discrepant results were retested by a new version (HC02) extended to types 4, 5 and 6. RESULTS: The distribution frequency of HCV genotypes was subtype 1a, 16.4%; subtype 1b, 46.3%; subtype 2a, 7.5%; subtype 3a, 20.9%; type 4, 4.5%; type 5, 0.7%; and co-infections, 3.7%. Among all the patients, 95% were of type 1, 2 or 3. The antibody reactivities of hemodialysis (1/7; P < 0.05) and HIV-seropositive patients (4/9; P = 0.06) were lower than for the patients seen at the hepatology unit (87/118). For these latter patients, the serotyping assay was interpretable in 71% and concordant in 64% of the samples with the genotyping assay. Out of the 84 samples with interpretable results, 75 sera were correctly serotyped (89% specificity). The two mixed results obtained by serotyping did not correspond to genotype co-infections (n = 3) and reciprocally. Six discrepancies were ruled out by the new assay, but the 2 untypeable sera remained unsolved, and four out of six sera with genotype 4 were serotyped as type 5. CONCLUSIONS: Serotyping could be an attractive approach if the reactivity was improved and the subtyping possible.

Adult↗
PubMed1997

[Research of type 1, 2 and 3 hepatitis C virus specific antibodies in relation to the viral genotype in chronically infected patients].

The determination of the viral genotype in chronically HCV infected patients is used as an epidemiologic tool, a predictive marker of the evolution of the disease and especially of the response to the interferon alfa therapy. Its determination needs an amplification of the selected genomic region and remains expensive. Thus an indirect determination of the genotype has been proposed using the characterization of type-specific antibodies. In 101 chronically HCV infected patients, a serologic method specific for HCV type 1, 2 and 3 has been evaluated in relation to the genotyping one. The test was interpretable in 64 sera and in agreement with the genotyping method in 92% of the samples. The reactivity of the test was lower in hemodialysis and IVDUs patients (p < 0.02). The mixed results obtained by the serologic typing method were not in agreement with the results of the genotyping coinfections. We could not differentiate the possible past infections from the cross-reactivities of the test. The serotyping methods was simple and rapid, allowing generally a deduction of the viral genotype. It could be an attractive approach if the reactivity was improved and the subtyping was possible.

Adult↗
PubMed1996

Homology among nearly all plasmids infecting three Bacillus species.

We have surveyed naturally occurring plasmids in strains of Bacillus subtilis and the closely related species B. mojavensis and B. licheniformis. Previous studies have failed to find host-benefitting functions for plasmids of these species, suggesting that these plasmids are nonmutualistic. Only one type of plasmid was found in each plasmid-bearing strain, suggesting that most of the plasmids infecting these Bacillus species are in the same incompatibility group. A sample of 18 plasmids from these species ranged in size from 6.9 to 16 kb, with all but 6 plasmids falling into three size groups. These groups differed in the sizes of their host ranges and geographical ranges. All but 1 of the 18 plasmids from these three host species are homologous with one another. The cryptic plasmids from these three species are far less diverse than are plasmids (from other species) that are known to benefit their bacterial hosts. The low-level diversity among these cryptic plasmids is consistent with the hypothesis that host-benefitting adaptations play an important role in fostering the coexistence of plasmid populations, but other explanations for the low-level plasmid diversity are possible. Comparison of the phylogenies of the plasmids with those of their hosts suggests that Bacillus plasmids are horizontally transferred in nature at a low rate similar to that found for the colicin plasmids of Escherichia coli.

Bacillus↗
PubMed1995

The log-linear relationship between sexual isolation and sequence divergence in Bacillus transformation is robust.

The relationship between sexual isolation and sequence divergence in Bacillus transformation was previously shown to be log linear. In the present study, we have shown that this relationship is robust with respect to naturally occurring genetic variation among recipient strains of Bacillus subtilis and B. mojavensis. Naturally occurring restriction endonuclease activity was shown not to affect this relationship. Also, seven out of eight recombination mutants tested for their sensitivity to sequence divergence have shown the same relationship between sequence divergence and sexual isolation; a mutant for recH was more sensitive to sequence divergence, suggesting that the product of this gene may be involved in resolution of mismatches in heterogamic transformation. We have also shown that the relationship between sexual isolation and sequence divergence is robust with respect to variation in the conditions of transformation, including variation in the length of donor DNA, the concentration of donor DNA, and intracellular competition between donor-derived and recipient-derived DNA. The robustness of the relationship between sexual isolation and sequence divergence among naturally occurring strains and across transformation conditions allows us to predict the eventual outcome of sequence divergence among B. subtilis and its closest relatives.

Bacillus↗
PubMed1995

The size and continuity of DNA segments integrated in Bacillus transformation.

We investigated the size and continuity of DNA segments integrated in Bacillus subtilis transformation. We transformed B. subtilis strain 1A2 toward rifampicin resistance (coded by rpoB) with genomic DNA and with a PCR-amplified 3.4-kb segment of the rpoB gene from several donors. Restriction analysis showed that smaller lengths of donor DNA integrated into the chromosome with transformation by PCR-amplified DNA than by genomic DNA. Nevertheless, integration of very short segments (< 2 kb) from large, genomic donor molecules was not a rare event. With PCR-amplified segments as donor DNA, smaller fragments were integrated when there was greater sequence divergence between donor and recipient. There was a large stochastic component to the pattern of recombination. We detected discontinuity in the integration of donor segments within the rpoB gene, probably due to multiple integration events involving a single donor molecule. The transfer of adaptations across Bacillus species may be facilitated by the small sizes of DNA segments integrated in transformation.

Bacillus subtilis↗