Les concentrations sous-inhibitrices (sub-CMI) de antibiotiques jouent un rôle important dans la sélection et le développement des résistances. Contrairement à Escherichia coli, Vibrio cholerae induit la réponse SOS en présence de sub-CMI d'aminosides. SOS est également impliquée dans la plasticité du génome et dans l'acquisition de la résistance aux antibiotiques. Afin de sélectionner des mutants de V. cholerae qui n'induisent pas SOS en présence de sub-CMI d'aminosides, nous avons développé un crible génétique pour l'isolement de mutants dans lesquels l'induction de la réponse SOS est perdue. L'un de ces mutants est inactivé pour le gène radD, qui code pour une hélicase ADN/ARN putative. RadD est impliquée dans la résolution de cassures d'ADN double brin (DSB) provoquées par des sub-CMI de tobramycine. Nous avons montré que les R-loops sont à l'origine des DSB formés en absence de radD en tobramycine. Nous suggérons que les lésions de l'ADN formées lors du traitement par aminoglycosides soient réparées par la formation d'intermédiaires ssDNA induisant SOS. L’ARNPol bloquée sur ces lésions peut faciliter la formation de R-loops qui, si elles ne sont pas réparées, peuvent entraîner la formation de DSB et l'instabilité du génome. RadD pourrait jouer un rôle dans la résolution des R-loops. Ces résultats ont mis en évidence le fait que les sub-CMI de tobramycine conduisent à DSB, dues en partie aux R-loops. La tobramycine est un aminoside qui cible le ribosome. La formation de DSB par un tel antibiotique peut être surprenante car la formation de lésions de l'ADN par un antibiotique qui cible la traduction n'est pas attendue. Afin de comprendre les voies impliquées dans la réponse à de sub-CMI de tobramycine, nous avons adopté une approche Tn-seq à haut débit pour déterminer quels gènes sont importants pour maintenir l'intégrité de la cellule en présence d'antibiotiques à faibles doses. / Sub-inhibitory concentrations (sub-MIC) of antibiotics play an important role in selection and development of resistances. Unlike Escherichia coli, Vibrio cholerae induces its SOS response in presence of sub-MIC aminoglycosides. SOS is also involved in genome plasticity and in the acquisition of resistance to antibiotics. In order to select for V. cholerae mutants that do not induce low aminoglycoside-mediated SOS induction, we developed a genetic screen for the isolation of mutants in which induction of the SOS response by sub-MICs of aminoglycosides is lost. One of these mutants is inactivated for the radD gene, which encodes a putative DNA/RNA helicase. RadD is involved in the resolution of double strand DNA breaks caused by treatment with sub-MIC of tobramycine. We demonstrate that R-loops are at the origin of DSBs formed in the absence of radD in tobramycine.We propose that DNA lesions formed upon aminoglycoside treatment are repaired through the formation of ssDNA intermediates, inducing SOS. RNAP could stalls on these lesions and forms R-loops, that, if not repaired, can lead to the formation of DSB and genome instability. RadD could play a role in the resolution of R-loops. These results highlighted the fact that sub-MIC of tobramycine leads to DNA double strand breaks, at least partly through R-loop formation. Tobramycin is an aminoglycoside that targets the ribosome. The formation of DSBs by such an antibiotic can be surprising as DNA damage formation by an antibiotic that targets translation is not expected. In order to understand the pathways involved in the response to low doses of tobramycin we adopted a high throughput Tn-seq approach to determine which genes are important in maintaining the integrity of the cell in the presence of antibiotics at low doses.

This study intends to examine a ninth century anti-Christian polemic work written by the great Muslim litterateur al-Jaḥiẓ. The historical background of the treatise is presented within the contexts of the early `Abbasid regime (750-900), the Christian communities of the time, the impact of the translation movement, the rise and development of polemic discourse between Muslims and Christians, and the life and works of al-Jaḥiẓ. The study provides the manuscript background of the letter along with a translation supplemented by the work of Joshua Finkel. The analysis of the work is limited to one section, which reflects al-Jaḥiẓ's most original contribution to antiChristian Muslim polemic. The actual analysis is focused thematically in order to better ascertain al-Jaḥiẓ's portrayal of Christians before his Muslim readers.

Univ., Diss.--Bochum, 2001.

No description available.

Dental plaque forms sequentially, with Fusobacterium nucleatum facilitating the adhesion of pathogenic late colonizers. We hypothesize that a single-chain variable fragment (scFv) antibody library will enable the identification of F. nucleatum adhesins and help elucidate the molecular mechanisms of coaggregation between F. nucleatum and other bacteria. A 4X10^8 clones scFv phage display library was created using spleen RNA from a mouse immunized with F. nucleatum. The library was enriched by biopanning against F. nucleatum 6 times and 292 individual clones tested by ELISA reacted strongly to F. nucleatum. Sixty-two of those clones inhibited F. nucleatum coaggregation with Streptococcus sanguinus. Analysis of select clones revealed differences in coaggregation inhibition, recognition of outer membrane proteins, and BstOI restriction pattern. DNA sequencing showed 6 unique scFvs and of them 3 strongly inhibited interaction with 5 Streptococcus species. These scFvs recognize the outer membrane autotransporter protein RadD (Fn1526), as determined by mass spectrometry. / Farhan Khan placed second in the International Association for Dental Research/Unilever Hatton Competition in the Senior Basic Science Research Category representing Canada, while presenting the research contained in this dissertation. This international competition took place during the 90th General Session & Exhibition of the International Association for Dental Research in Iguaçu Falls, Brazil in June 2012.