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Pseudomonas
aeruginosa
is an important bacterial pathogen in Western society; it is the third
leading cause of hospital-associated (nosocomial) infections, causing many
deaths in hospitalized patients, and is the leading cause of eventually
fatal lung infections in patients with the genetic disease,
cystic fibrosis. It is difficult to treat infections caused by this
pathogen largely because antibiotics can be ineffective. For more than two
decades we
have been involved in a broad range of projects on this organism, in
particular with respect to its outer membrane permeability, intrinsic
resistance to antibiotics and outer membrane proteins. However since the
2001 the sequencing of the Pseudomonas genome we have dramatically
changed our approach to studying this organism. Thus we now utilize a series
of functional genomic approaches. |
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 Genomics
We were associated with the original
genome sequencing effort, in particular the annotation of the Pseudomonas aeruginosa
PAO1 reference genome. In particular we were involved in coordinating a
Pseudomonas aeruginosa research community annotation project called
PseudoCAP. This is described elsewhere at
http://cmdr.ubc.ca/bobh/PAAP.htm.
The lab is
also, with the assistance of Fiona Brinkman at SFU, hosting the
Pseudomonas aeruginosa
web page. Since the genomics publication we were involved in
establishing a series of tools to permit post genomic studies. These
included the establishment of microarrays to probe transcription of all
genes in P. aeruginosa, the development of a compendium of the secreted
proteins of this organism through 'PhoA fusion technology, and development
of a
mutant library using lux-fusion technology.
Outer
membrane proteins
We
originally demonstrated that low outer membrane permeability due to the poor
functioning as a pore of porin OprF, accounted substantially for generalized
antibiotic resistance in P. aeruginosa. A combination of
biophysical-biochemical, molecular genetic, structural, bioinformatic and
genomic approaches have been utilized to study the structure:function
relationships of major porin and adhesin OprF, the phosphate-selective porin
OprP, the PhoPQ-regulated protein OprH, the 18-member OprD family of
substrate-selective porins, and the 19-member family of homologs of the
efflux porin OprM. Certain of these porins also have a role in antibiotic
uptake/efflux, e.g. OprD in specific imipenem uptake/resistance, OprF in
general passage of antibiotics, and OprM together with its cognate linker &
pump components MexAB in intrinsic resistance to antibiotics. As part of our
contribution to the Pseudomonas Genome Project, we have set up a reference
web site listing known and putative
P. aeruginosa
outer membrane proteins.
Analysis of the recently-published
P. aeruginosa genome sequence indicated several large families of
proteins most of which are paralogs of genes which we have studied
intensively, e.g. the beta-lactam imipenem-selective porin OprD [19
proteins], the multidrug-efflux outer membrane protein OprM [18 proteins],
the iron-regulated outer membrane proteins [32 proteins], and the ECF sigma
factor family [21 proteins] homologous to SigX which regulates expression of
the major outer membrane porin OprF.
More recently we defined the
functions of many members of the family of porins related to OprD.
The substrate specificities of 7 OprD homologues were
inferred using studies of the growth specificities of mutants, the
regulation of encoding genes and the genomic context. The specificities
determined were as follows: OpdK - vanillate, OpdP - glycine-glutamate, OpdC
- histidine, OpdB - proline, OpdT - tyrosine, OpdH - cis-aconitate,
and OpdO - pyroglutamate.
Virulence
Access to a broad series of
functional genomic tools has permitted us to perform detailed studies on
certain aspects of virulence. In addition to our studies of two component
regulators that are described in more detail under "Two Component Regulators
of Resistance", we have been particularly interested in motility (especially
swarming motility) and adherence.
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