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Title: Putative bacteroides fragilis virulence determinants; analysis and comparison
Author: Moore, Jane
Awarding Body: Queen's University Belfast
Current Institution: Queen's University Belfast
Date of Award: 2007
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Bacteroidesfragilis forms part of the gastrointestinal microbiota. On release from the gastrointestinal tract this opportunistic pathogen can cause internal abscesses and bacteraemia. Completed genome sequences of B. fragi/is NCTC 9343, 638R and YCH46 recently became available. Therefore the importance of potential virulence factors may be assessed though genotypic and phenotypic comparisons. B. fragilis NCTC 9343 phase variably expresses a large capsule (LC), small capsule (SC) and an antigenically variable electron dense layer (EDL). A small irregular LC like capsule is expressed by B. fragilis 638R, attributed to a stop codon within BF2782 (putative polysaccharide export protein). Phase variable LC expression may be regulated by excision/insertion of a transpos~n, detected in PS-9/I of B. fragilis YCH46. The EDL polysaccharides produced by the 3 strains are divergent. This has no effect on in vivo survival. The conservation of invertible promoter regions (fIX sites) and putative transcriptional regulators, upxZ and upxY, indicates antigenic variation may be important for virulence. Invertases, finA and finB are involved in inversion of the fIX sites. The presence of . finA is conserved but notfinB. A long delay is observed prior to detection of antigenic variation in finB+ B. fragilis NCTC 9343, but not finE B. fragilis LS66. Therefore finB may be repressing inversion of the fix sites. The absence offinB, LC expression, haemagglutination phenotype, or reduced growth rate in a minimal medium does not affect in vivo survival. Iron acquisition and regulatory systems are important for B. fragilis virulence, with the ferric uptake protein, FeoAB, and ferric uptake regulator, Fur, required for B. fragilis survival in vivo. FeoAB is important for growth of B. fragilis in vitro, indicating ferrous iron is an important iron source. The haem uptake protein, HutA, and the peroxide regulon repressor, Per, are not required for B. fragilis survival in vivo.
Supervisor: Not available Sponsor: Not available
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID:  DOI: Not available