Analysis of the role of fimbriae in the virulence of Salmonella enterica in poultry

Clayton, Debra Jayne (2008) Analysis of the role of fimbriae in the virulence of Salmonella enterica in poultry. PhD thesis, University of Glasgow.

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Abstract

Salmonella is a Gram-negative bacterium that consists of two species; S. enterica and
S. bongori. The species S. enterica can be further divided into 6 subspecies and
subspecies I is predominantly associated with disease in warm blooded animals and
contains over 2,500 antigenically distinct serovars. Each serovar is >90% identical at
the DNA level but can infect a different range of hosts and cause different diseases.
Poultry are an important reservoir of entry of Salmonella into the human food chain
owing to the contamination of their eggs and meat. The molecular mechanisms
underlying colonisation of food producing animals with Salmonella are unknown.
Fimbrial genes encode proteinaceous surface exposed appendages which have been
shown to mediate adhesion of bacterial cells but the precise role for fimbriae in the
carriage and virulence of Salmonella is poorly defined.
The purpose of this study was to annotate and characterise the fimbrial genes of the
poultry-associated S. enterica serovars Enteritidis and Gallinarum and relate this role to
host-specificity. The availability of the genome sequences of several strains of S.
enterica allowed a comparison of the sequence, location and repertoire of fimbrial genes
and although no unique fimbrial genes were identified all serovars possessed a unique
repertoire. The host-specific serovars contain a higher number of pseudogenes within
fimbrial operons than the ubiquitous serovars and the rate of attrition of fimbrial genes
was 3-4 fold higher than the genomic mean. Such gene decay may partially explain the
narrowing of host-range of the host-restricted and host-specific serovars.
Polymorphisms that may alter transcription were identified along with targets that may
be associated with phase variation of the fimbrial genes.
Lambda red-mediated homologous recombination was used to construct a panel of S.
Enteritidis P125109 and S. Gallinarum 287/91 strains lacking major fimbrial subunit genes which were examined in vitro and in vivo. Several fimbrial subunits played a role
in the adherence to and invasion of different cell lines in different growth conditions and
the role appeared to be serovar-specific. A mutation in the steA gene impaired
interactions with different cell lines in vitro but this phenotype was found to be due to a
polar effect on genes downstream of steA. The majority of fimbrial subunits played no
significant role in the colonisation of the alimentary tract in an established chicken
model. Mutation of the stcA gene resulted in the greatest degree of attenuation in vivo
of all of the fimbrial mutants examined. This phenotype was trans-complemented and
was not the result of a polar or second-site defect thereby fulfilling molecular Koch’s
postulates. The stcA genes therefore play a significant role in the colonisation of the
chicken caeca.

Item Type: Thesis (PhD)
Qualification Level: Doctoral
Subjects: S Agriculture > SF Animal culture > SF600 Veterinary Medicine
Colleges/Schools: College of Medical Veterinary and Life Sciences > School of Veterinary Medicine
Supervisor's Name: Supervisor, not known
Date of Award: 2008
Depositing User: Mrs Marie Cairney
Unique ID: glathesis:2008-4200
Copyright: Copyright of this thesis is held by the author.
Date Deposited: 19 Apr 2013 08:36
Last Modified: 19 Apr 2013 08:38
URI: http://theses.gla.ac.uk/id/eprint/4200

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