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dc.contributor.authorTotsika, Makrinaen
dc.date.accessioned2018-05-22T12:49:10Z
dc.date.available2018-05-22T12:49:10Z
dc.date.issued2007en
dc.identifier.urihttp://hdl.handle.net/1842/30851
dc.description.abstracten
dc.description.abstractUropathogenic Escherichia coli (UPEC) are the etiologic agent of more than 80% of uncomplicated urinary tract infections (UTIs) in humans. Pyelonephritis-associated pili (Pap) are fimbrial adhesins that facilitate binding of UPEC to Gala-(l,4)-Gal/i moieties contained in membrane glycolipids on human uroepithelial cells and are associated with acute kidney infection (pyelonephritis). Pap expression is phase variable and the frequency with which phase transition occurs determines the proportion of P-fimbriate bacteria in the population. In this study, pap phase transition frequencies were measured in clinical isolates for the first time and were shown to be markedly higher than the frequencies displayed by the same pap operons measured in E. coli K-12. In this relevant regulatory context, phase variation frequencies of homologous pap operons were found to be differentially affected by culture conditions, indicating a hierarchy of expression depending on environmental signals. Cross-talk between pap operons was also found to be dependent on culture conditions. The molecular mechanism leading to different phase variation frequencies between homologous pap operons was investigated by sequencing 82 pap regulatory regions and their regulators (papl and papB) from 54 UPEC isolates of different clinical origin (asymptomatic vs. symptomatic UTI). One variable region identified was a high affinity binding site for the pap autoregulatory protein PapB. The site contained a variable number of 9 bp repeats with (T/A)3 sequences, which affected PapB binding and the frequency of off-to-on phase transition, under particular environmental conditions. Sequence diversification via point mutation was also observed among papl genes, encoding for the pap transcriptional activator Papl, and were shown to be under positive selection (dN/dS > 1) for functionally adaptive amino acid replacements. Certain Papl variants correlated with symptomatic disease and differed in their ability to activate pap operons. This study provided different lines of evidence supporting the hypothesis that UPEC isolates have evolved mechanisms to regulate the phase variation frequencies of homologous fimbrial operons, potentially to achieve their differential activation and sequential expression. The ability of UPEC to coordinate expression of multiple surface factors is critical for the successful colonisation of the varied complex micro-environments encountered in the human urinary tract.en
dc.publisherThe University of Edinburghen
dc.relation.isreferencedbyAlready catalogueden
dc.subjectAnnexe Thesis Digitisation Project 2018 Block 19en
dc.titleRegulation of fimbrial phase transition frequencies in uropathogenic Escherichia colien
dc.typeThesis or Dissertationen
dc.type.qualificationlevelDoctoralen
dc.type.qualificationnamePhD Doctor of Philosophyen


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