Ismail, Asma
(2011)
Molecular and immunological profiling of typhoid carriers and salmonella typhi:
towards development of preventive and investigative diagnostics.
Molecular and immunological profiling of typhoid carriers and salmonella typhi: towards development of preventive and investigative diagnostics.
(Submitted)
Abstract
Detection of typhoid carriers is not easy due to the lack of effective lab tests for
carriers. If we can design diagnostic tests to detect for carriers, we can provide
treatment, create a carrier registry and study the carriers himself/herself -
(Fundamental and clinical studies), isolate S.Typhi from the carriers, sequence
its DNA and compare that to those isolated from acute cases - (Molecular
studies). In fact many studies (goldmine) can be done if we can detect for
carriers.
In this proposal we undertake to study individuals who were previously culture
positive for Salmonella Typhi for a minimum of 1 year with respect to the
following objectives:
• To develop new methods to identify possible carriers
• To determine the OMP antigens that are antigenically specific to
typhoid carriers
• To determine the immunological factors that predispose individuals
to become carriers
• To sequence and compare the DNA profiles of S. Typhi isolated
from acute cases, carrier cases, the environment and the S. Typhi
DNA sequence (gene bank)
• To develop diagnostics for detection of typhoid carriers
• Perform evaluation of the developed tests
Among the achievements of studies include:
Establishing the first carrier registry in Kelantan/Malaysia
Our PCR assay could match the culture results suggesting our PCR test
could be an alternative method to detect for carriers
When screened for biomarkers, the carrier lgG and lgA showed that it
recognized only the 50kDa antigen of S.Typhi. The TYPHIDOT-C was
shown to be a potential serological screening tool to detect for possible
carriers.
Established the first genome sequence bank of S.Typhi that are isolated
from confirmed carriers from Malaysia (MyTyphoidgenom). The specific
sites could not be considered of value as epidemiological markers as well
as diagnostic purposes since they are no unique sequences for S. Typhi
isolated from typhoid carriers. This revealed that typhoid carriage is NOT
due to the organism but rather due to host factors.
Immunological profiling of the host showed that reduced levels of TH1 and
TH2 cytokines might suggest a carrier status
The candidate gene (2136 bp Polynucleotide phosphorylase gene) was
used to test if typhoid carrier state in humans was due to a mutation in this
gene that was reported to determine virulence and carrier status of S.
Typhimurium in mice. Results showed that there were 11 silent mutations
in the PNPase gene (hence did not affect protein expression). Hence the
findings reported for S, Typhimurium in mice cannot be extrapolated to
S.Typhi that affect only humans
In developing the dipstick method for Antibody carrier detection, we have
shown by POC that the dipstick method is working in our laboratory for
detection of lgA. When outsourced for the cassette format for both lgG
and lgA requires more time for fine tuning.
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