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34 35 > Research Report // AR 2006
One aim of the group is to determine how HSV is assembled
on to identify the first VZV encoded anti-apoptotic gene
Oral bacteria and infective endocarditis
porphyrin macrocycle and therefore must obtain this from
within cells at the molecular level. Recent work has identified
ORF63. To further our understanding of VZV with human
Streptococcus gordonii is a primary coloniser of oral
tissue sources, usually from haem-proteins that may also
crucial molecular interactions required for viral assembly.
nerve cells the group has developed a novel model of VZV
microbial biofilms. This organism is considered to be
supply iron. Research at the institute has identified the so-
Such information on viral assembly will allow development
infection of intact human explant ganglia. The group has
beneficial in the oral environment but pathogenic when it
called HA2 receptor as a porphyrin receptor important in the
of inhibitors of this process which may be candidates for use
shown for the first time that VZV can infect intact human
colonises heart valves as this results in infective endocarditis.
acquisition and surface storage of haem. In recent work this
as antivirals for control of recurrent herpes simplex.
ganglionic cells and this is a novel way of studying the
There is considerable interest in attempting to engineer
receptor mechanism was effectively used to selectively target
The group also aims to examine the mechanism(s) involved in
the entry, axonal transport, assembly and exit of HSV-1 from
neurons. The group’s studies have shown how HSV can travel,
assemble and exit from specialized sites along human nerves.
Another aim of the group is to determine how HSV and
HIV are transported within cells at the molecular level.
Recent discoveries have shown how virus transport in cells
is dependent on interactions between specific viral proteins
and cellular “motor proteins” and how in the case of HSV
the virus escapes from nerves to infect skin and cause disease.
Such information on viral transport will allow development
of inhibitors of this process which may be candidates for use
as antivirals for control of recurrent herpes simplex or HIV.
Varicella zoster virus
Despite its significant impact on the community, little is
known about the molecular basis of the Varicella zoster
virus (VZV), due in part, to VZV only infecting humans.
To more closely examine the interaction of VZV with host
cells, the group has established several models of infection
using human cell-types which are targets for infection and
are relevant to those that suffer from either Varicella or herpes
zoster/PHN because each of these cell types are likely to play
different, but essential roles in the disease process. These
include human fibroblasts (skin cells), neurons (nerve cells)
and specialized immune cells (T cells and dendritic cells).
The group has recently shown that human nerve cells
infected with VZV do not undergo programmed cell death
(apoptosis). This is an important finding because it suggests
the nerve cell damage observed when VZV reawakens from
its “silent” state in nerve cells to cause shingles is not due
to programmed cell death. Another implication from this
observation is that VZV encodes a function to interfere with
the death response in human nerve cells, thus providing
a possible mechanism by which the virus can establish
and maintain its life-long dormant infection. We went
interaction of this virus with human nerve cells.
These features of intact ganglionic infection can now be
studied in further detail to better define the molecular
mechanisms that underlie VZV infection of ganglionic cells.
For example, this model provides a means to rapidly test
viral gene mutant viruses and new candidate vaccine strains
containing targeted gene disruptions to define viral genes that
may play critical roles in VZV neurotropism and to examine
in detail the outcome of infection of both neurons and nonneuronal
cells with respect to apoptosis and cell function.
Institute of Dental Research
Proteomics and structural genomics of oral pathogens
The difficulty in preventing dental caries results from the
need to devise a strategy to eliminate key cariogenic species
without disrupting the overall complexity of the protective
biofilm community on teeth. Solving this problem is at
the forefront of research at the institute. The completion of
a comprehensive series of comparative proteome studies,
involving both planktonic and biofilm grown cells, has
highlighted a number of biochemical events that are unique
for the survival of the cariogenic pathogen, Streptococcus
mutans, that proliferates under acidic conditions in dental
plaque. Genes implicated in these adaptive responses,
including alteration in acid tolerance and biofilm formation,
are being systematically examined using a functional
genomics approach. By defining the critical events associated
with the survival and proliferation of S. mutans under
conditions that lead to enamel dissolution, researchers at
the Institute are gaining the necessary knowledge to develop
a comprehensive strategy for intervention, thus allowing
appropriate susceptible biochemical events to be targeted to
control or eliminate disease.
this bacterium to be both non-pathogenic and to resist
displacement by oral pathogens such as Streptococcus
mutans. In vitro gene expression technology has identified the
gom locus comprising a regulon of 15 open reading frames
implicated in bacterial growth, beneficial adhesion to the tooth
surface, and pathogenic colonisation of heart valves. Analysis
of this locus by researchers at the institute has focused on a
group of novel glycosidases within the gom locus with the
3D-structure of the first of these, GcnA, recently having being
solved at high resolution. Current research is directed at the
selective inhibition of this glycosidase as well as to determining
the structure and function of other products of the gom locus
including two related glycosidases that are also implicated in
infective endocarditis.
Polymicrobial aetiology of caries progression
In studies at the institute, some eighty bacterial species
were detected within the polymicrobial consortia of carious
dentine that overlies the pulp following an extension of the
enamel lesion of dental caries. However, recent studies have
shown that pulpal infection, arising from end-stage disease, is
far more selective. By using fluorescence in situ hybridisation
(FISH), the complex consortia of bacteria associated with
carious dentine has been shown to mass at the periphery of
the soft tissue, with only a few species invading. Currently,
the structural framework and spatial arrangement of bacterial
invasion is being mapped. While clinically important from
a dental perspective, this process also provides a rare insight
into the dynamics of polymicrobial infections that impact
severely on human health, particularly chronic infections.
Targeted control of oral pathogens
Competition for iron is considered to be a central event in
many infections. A number of pathogenic bacteria have
acquired complex mechanisms to sequester iron, often from
haem. The periodontal pathogen, Porphyromonas gingivalis,
is unusual in that it has lost the capacity to synthesise the
and inhibit this bacterium with custom synthesised modified
porphyrin-antibiotic conjugates. More recently, a number of
other haem binding proteins that are located on the surface
of the organism have been identified and are being studies
in order to expand the range of targets for inhibition by
exploiting those aspects of porphyrin storage and transport
that are unique to P. gingivalis.
Determinants of oral infection in high-risk
aboriginal communities
Anaerobic Gram negative bacteria have been determined
to be numerically important in relation to the early onset
and high incidence of periodontal disease in an Aboriginal
community. Research at the institute has suggested that
early mucosal colonisation of infants with pathogenic
porphyromonads act as release sites for transmission of these
organisms within families. Biotyping of Porphyromonas
gingivalis strains based on variations in the lysine-gingipain
gene indicated skewing of biotype distribution in the
Aboriginal community compared with that observed in
metropolitan cohorts. Further evidence for the presence
of characteristic discriminatory flora within the Aboriginal
community was obtained by microbial population analysis
based on molecular phylogeny. These observations have
provided a basis for ongoing dissection of the microbial risk
factors for oral infection that prevail in such a high risk group
and underpin proposed strategies to break the cycle of disease
by preventing transmission to infants. Additionally, there is
no information to determine whether disease susceptibility
amongst Aborigines reflects organisms that have been
associated with Aboriginal people for millennia or if there
is a pathogenic influence from organisms acquired, most
probably, from Anglo-Saxon settlers. As there is little genomic
information for these mucosal pathogens, assessment of the
origin and heterogeneity of organisms within communities
is being assessed by analysis of a matrix of highly conserved
house-keeping genes. This will both establish the relative