Diagnostic Methods for Mycobacterium tuberculosis and Challenges in Its Detection in India

Abstract

Tuberculosis (TB) is one of the world’s oldest and most important disseminating infectious diseases that still accounts for a high morbidity and mortality among adults. Despite high prevalence, case detection rates are low, posing major hurdles for TB control in developed and developing countries. Traditional diagnosis of TB bacilli depends upon smear positivity in sputum samples, culture and chest radiography. All these tests have known limitations. Conventional tests for detection of drug resistance are slow, tedious and difficult to perform in field conditions. For rapid diagnosis, new methods include newer versions of nucleic acid amplification tests, immune-based assays, skin patch test and rapid culture systems. For drug resistance analysis line-probe assays, bacteriophage-based assays, molecular beacons and microscopic observation drug susceptibility assay are available. An ideal test for TB is still not available and fast emergence of drug resistant tubercle strains aided by the everincreasing HIV AIDS-epidemic in third-world countries has stressed the need of rapid diagnostic test(s) to show the presence of mycobateria in the clinical samples. Microscopy and culture are still the major backbone for laboratory diagnosis of tuberculosis; new methods including molecular diagnostic tests have evolved over a period of time. The majority of molecular tests have been focused on: (i) detection of nucleic acids both DNA and RNA, which are specific to Mycobacterium tuberculosis, by amplification techniques such as polymerase chain reaction (PCR) focusing on detection and molecular epidemiology of M. tuberculosis; and (ii) detection of mutations in the genes which are associated with resistance to anti-tuberculosis drugs by sequencing or nucleic acid hybridization. The development and use of rapid diagnostic tools become increasingly important in addressing the emergence and treatment of multi-drug resistant (MDR) and extreme-drug (XDR) resistant M. tuberculosis strains.