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Caractérisation d'éléments conjugatifs intégratifs (ICE) chez Mycoplasma hominis

Abstract : Mycoplasmas are small-genome bacteria derived from Gram-positive ancestors by a succession of genetic material losses. It has long been considered that genetic reduction was the only force governing the evolution of these bacteria, however, horizontal transfers of large chromosomal regions within and between mycoplasma species have recently been reported. Conjugative and integrative elements (ICE) found in some species of mycoplasma may be responsible for these transfers. These ICEs encode the systems necessary for excision, conjugative transfer and integration into a recipient cell.Mycoplasma hominis is a commensal genital mycoplasma that can be responsible for gynecological infections, neonatal infections and extragenital infections. Preliminary analysis of M. hominis genomes had showed the presence of coding regions characteristic of ICEs. The objectives of this thesis were to search for and characterize ICEs in one reference strain and 11 fully sequenced M. hominis clinical isolates and to determine the prevalence of these ICEs in the M. hominis species. To do so, a retrospective study over a period of 6 years was conducted on clinical isolates collected at the Bordeaux University Hospital. The minimum inhibitory concentrations of tetracyclines and fluoroquinolones as well as resistance mechanisms were determined, providing a collection of clinical isolates characterized for the study of ICEs.ICEs of 27-30 kpb were found in one or two copies in seven of the 12 M. hominis sequenced strains. Only five of these ICEs seemed functional since circular forms of extrachromosomal ICE were detected. All M. hominis ICEs exhibited a similar structure consisting of a 4.0-5.1 kb module composed of five to six juxtaposed CDSs, encoding proteins that share common structural features with transcription activator-like (TAL) effectors, involved in polynucleotide recognition and signal transduction in symbiotic bacteria. The characterization of antibiotic resistance mechanisms in M. hominis clinical isolates collected at Bordeaux University Hospital enabled us to obtain a collection of 183 isolates isolated between 2010 and 2015, of which 14.8% harbored the tet(M) gene responsible for tetracycline resistance, 2.7% were resistant to levofloxacin and 1.6% were resistant to moxifloxacin by mutation in topoisomerase IV and DNA gyrase genes. Screening of 120 of these clinical isolates revealed a high prevalence of ICEs in M. hominis, measured to be 45%. The proportion of ICEs was not higher in isolates carrying the tet (M) gene, suggesting that ICEs were not responsible for the spread of tetracycline resistance.Additional mating experiments will be necessary to confirm the functionality of the ICEs found in the M. hominis species. However, the conserved and specific structure of M. hominis ICEs and the high prevalence in clinical strains suggest that these ICEs may confer a selective advantage for the physiology or pathogenicity of the bacteria. This work opens the way for future studies that will provide a better understanding of horizontal gene transfers and virulence factors in M. hominis.
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Alexandra Meygret. Caractérisation d'éléments conjugatifs intégratifs (ICE) chez Mycoplasma hominis. Médecine humaine et pathologie. Université de Bordeaux, 2019. Français. ⟨NNT : 2019BORD0177⟩. ⟨tel-02399550⟩

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