Faster diagnostic tests
developed for tuberculosis
By Dr. Divya Khatter
T
uberculosis (TB) claims
two million lives each year
globally. Early detection
and treatment are crucial
to prevent spread, outbreaks, and
development of resistance. Scientists
at the Translational Health Science and
Technology Institute (THSTI) Haryana
and All India Institute of Medical
Sciences (AIIMS) New Delhi have
jointly developed highly sensitive and
rapid tests for detection of tuberculosis
infection in lungs and surrounding
membranes.
TB spreads from one person to
another through inhalation of infected
air. When the bacteria attacks the
lungs, the disease manifests itself
in a pulmonary form. It is the most
common form of TB. But about 15%
of new patients in 2016 were found
infected with extrapulmonary TB
where organs other than lungs may
be affected. Till now, detection of all
forms of TB is mostly based on sputum
smear microscopy and culture tests.
While smear microscopy is simple and
rapid, it has low sensitivity. Culture
test is highly sensitive, but takes 2 to 8
weeks to get results.
Conventional diagnostic tests use
antibodies for detection of bacterial
proteins in sputum samples. However,
such tests suffer with limitations
including batch-to-batch variability,
limited shelf-life, and cost.
To address these problems, the
researchers have now developed two
DNA aptamer-based tests - Aptamer
Linked Immobilized Sorbent Assay
(ALISA) and Electro Chemical Sensor
(ECS) for detection of a bacterial
protein in the sputum.
Aptamers are DNA, RNA or peptide
molecules that bind to specific
molecular targets. They are known to
bind the right target (which defines
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Volume 4 | Issue 1 | January-March 2019
sensitivity) and at the same time rule
out any non-specific binding to other
targets (specificity). The performance
of the newly developed tests was
compared with antibody-based tests
in 314 sputum samples. ALISA showed
92% sensitivity while the antibody-
based method was 68% sensitive.
The research team used ALISA to
detect a bacterial protein, HspX. This
method, however, took five hours to
yield results because it requires sputum
immobilization which is a time-
consuming step. So the team made
efforts to develop a simplified ECS
test. In this, aptamer was immobilized
with an electrode and upon binding to
HspX in the sputum sample, a drop in
the electrical signal was recorded.
The ECS test can be used for screening
of samples in the field as it takes as less
as 30 minutes to deliver results. It is
highly sensitive and could detect HspX
protein in 91% of the samples tested in
this study. In addition, there is no need
for sputum sample preparation which
is a complex and time-consuming
process.
The aim is to develop aptamers for
detection of multiple bacterial proteins
simultaneously which is expected to
lead a more robust test said Dr. Tarun
Sharma, a member of the research team.
The
aptamer-based
screening
tests
for
pulmonary TB, pleural
TB, and TB meningitis
hold immense promise
for a country like India,
where the disease burden
in high and primary
healthcare is only a
dream for many. The ECS
platform could be used
in a mobile screening
van at the point-of-care
explained Dr. Jaya Tyagi,
who led the research
team AIIMS hoping that these tests
are adopted by the TB programs in
the country.
The group used aptamer-based test
also for detection of pleural TB,
the second most prevalent form of
extrapulmonary TB. Early diagnosis
of pleural TB is limited by availability
of a sensitive and rapid test. The
performance of existing DNA-based
tests varies widely due to low bacterial
load in pleural fluid sample.
There is no test for making a confirmed
diagnosis of pleural TB. Even WHO-
endorsed Gene Xpert has a poor
sensitivity of 22%. On the contrary,
the aptamer-based test for pleural
TB has showed 93% sensitivity and is
cost-effective explained Dr. Sagarika
Haldar, a member of the research team.
The research teams were led by Dr.
Jaya Tyagi (AIIMS), Dr. Tarun Sharma
and Dr. Sagarika Haldar (THSTI)
including other colleagues from
the institutes. The pulmonary TB
results were published in the journal
ACS Infectious Diseases and the
pleural TB results were published in
Analytical Biochemistry. The studies
were funded by the Department of
Biotechnology, Department of Science
and Technology, and THSTI.
By India Science Wire