The multi-institutional team led by Prof. Jaya Sivaswami Tyagi from the Department of Biotechnology at AIIMS has developed a new diagnostic test for TB meningitis (the most severe form of TB) with nearly 100% of sensitivity and about 91% specificity. 87 cerebrospinal fluid samples obtained from pediatric subjects (39 TB meningitis patients and 48 controls) were analyzed to evaluate the efficiency of the diagnostic test. The study results were published lately in the journal Tuberculosis. Now the same technique has been adopted to diagnose pulmonary TB and pleural TB. The sensitivity of the test for pulmonary TB and pleural TB was 94% and 93% and the specificity was 100% and 98% respectively and the results are published in the journals ACS Infectious Diseases and Analytical Biochemistry. The diagnostic test is based on a derivative of a DNA aptamer. DNA aptamers are a single stranded DNA molecule and they bind to a specific target molecule and is a chemical rival of antibodies, that shows high binding affinity in nanomolar range and high specificity to a TB antigen known as HspX. Besides, higher binding affinity, there is significantly higher load of the HspX antigen in sputum and cerebrospinal fluid samples, leading to higher sensitivity. The antibodies must be generated in animals and they will not be of uniform quality, but aptamers can be produced in lab.
The researchers bound the aptamer to an electrode coated with gold nanoparticles and according to Dr. Tarun Kumar Sharma from Translational Health Science and Technology Institute (THSTI), Faridabad and the other corresponding author of the papers, “There is a drop in electrical signal if the sample is positive and no change in signal when the sample is negative.” Since the electrode is already immobilized with the aptamer, only the liquified sputum has to be added and the results can be obtained in 30 minutes. “Most time is taken to liquefy the sputum sample than the testing per se,” says Prof. Tyagi. In case of pleural TB samples, no sample processing is needed. The researchers have applied for the patent for the aptamer reagent and have licensed it to AptaBharat Innovation Pvt. Ltd. They are planning to validate the tests very soon on well characterized panel of specimens and field evaluation.
– Arpitha Shetty,