Epigenetic regulation of the nitrosative stress response and intracellular macrophage survival by extraintestinal pathogenic Escherichia coli.
Date
2011
Author
Advisors
Seed, Patrick C
Abraham, Soman
St. Geme, III, Joseph
Kreuzer, Kenneth
Valdivia, Raphael
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Abstract
Escherichia coli is a typical constituent of the enteric tract in many animals, including
humans. However, specialized extraintestinal pathogenic E. colistrains (ExPEC) may
transition from benign occupation of the enteric and vaginal tracts to sterile sites
such as the urinary tract, bloodstream, and central nervous system. ExPEC isolates
of urinary tract origin express type 1 pili as a critical virulence determinant mediating
adherence to and invasion into urinary tract tissues. Type 1 pili expression is under
epigenetic regulation by a family of site-specific recombinases, including FimX, which
is encoded from a genomic islet called PAI-X for Pathogenicity Islet of FimX. A goal
of this study was to determine the prevalence of the type 1 pili epigenetic regulator
genes (fimB, fimE, fimX, ipuA, ipuB) and associated PAI-X genes (hyxR, hyxA, hyxB)
present among an extended, diverse collection of pathogenic and commensal E. coli
isolates. Using a new multiplex PCR, fimX and the additional PAI-X genes were found
to be highly associated with ExPEC (83.2%) and more prevalent in ExPEC of lower urinary
tract origin (87.5%) than upper urinary tract origin (73.6%) or human commensal isolates
(20.6%; p < 0.05, all comparisons). Fim-like recombinase genes ipuA and ipuB also
had a significant association with ExPEC compared to commensal isolates, but had a
low overall prevalence (23.8% vs. 11.1%; p < 0.05). PAI-X also showed a strong positive
correlation with the presence of virulence genes in the genomes of pathogenic isolates.
Combined, our molecular epidemiology studies indicate PAI-X is highly associated with
ExPEC isolates, and its high prevalence suggests a potential role in the ExPEC lifestyle.
Further investigation into the regulation of PAI-X factors showed that FimX is also
an epigenetic regulator of a LuxR-like response regulator HyxR, encoded on PAI-X.
In multiple clinical ExPEC isolates, FimX regulated hyxR expression through bidirectional
phase inversion of its promoter region at sites different from the inversion sites
of the type 1 pili promoter and independent of integration host factor IHF. Additional
studies into the role of HyxR during ExPEC pathogenesis uncovered that HyxR is involved
in regulation of the nitrosative stress response. In vitro, transition from high to
low HyxR expression produced enhanced tolerance of reactive nitrogen intermediates
(RNI), primarily through derepression of hmpA, encoding a nitric oxide detoxifying
flavohemoglobin. However, in the macrophage, HyxR expression produced large effects
on intracellular survival in the presence and absence of RNI, and independent of Hmp.
Collectively, we have shown that the ability of ExPEC to survive in macrophages is
contingent upon the proper transition from high to low HyxR expression through epigenetic
regulatory control by FimX.
ExPEC reside in the enteric tract as commensal reservoirs, but can transition to a
pathogenic state by invading normally sterile niches, establishing infection, and
disseminating to invasive sites like the bloodstream. Macrophages are required for
ExPEC dissemination, suggesting the pathogen has developed mechanisms to persist within
professional phagocytes. This study demonstrates the functional versatility of the
FimX recombinase and identifies novel epigenetic and transcriptional regulatory controls
for ExPEC tolerance to RNI challenge and survival during intracellular macrophage
infection. Further investigation of these pathways may shed light on the regulatory
cues and programming that provoke the commensal to pathogen transition.
Type
DissertationDepartment
Molecular Genetics and MicrobiologySubject
AnimalsCell Line
DNA, Bacterial
Epigenesis, Genetic
Escherichia coli
Escherichia coli Proteins
Fimbriae Proteins
Gene Expression Regulation, Bacterial
Macrophages
Mice
Promoter Regions, Genetic
Reactive Nitrogen Species
Sequence Deletion
Sequence Inversion
Virulence Factors
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https://hdl.handle.net/10161/4999Citation
Bateman, Stacey Lynn (2011). Epigenetic regulation of the nitrosative stress response and intracellular macrophage
survival by extraintestinal pathogenic Escherichia coli. Dissertation, Duke University. Retrieved from https://hdl.handle.net/10161/4999.Collections
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