Rapid in vivo detection of isoniazid-sensitive Mycobacterium tuberculosis by breath test

There is urgent need for rapid, point-of-care diagnostic tools for tuberculosis (TB) and drug sensitivity. Current methods based on in vitro growth take weeks, while DNA amplification can neither differentiate live from dead organisms nor determine phenotypic drug resistance. Here we show the development and evaluation of a rapid breath test for isoniazid (INH)-sensitive TB based on detection of labelled N2 gas formed specifically from labelled INH by mycobacterial KatG enzyme. In vitro data show that the assay is specific, dependent on mycobacterial abundance and discriminates between INH-sensitive and INH-resistant (S315T mutant KatG) TB. In vivo, the assay is rapid with maximal detection of (15)N2 in exhaled breath of infected rabbits within 5-10 min. No increase in (15)N2 is detected in uninfected animals, and the increases in (15)N2 are dependent on infection dose. This test may allow rapid detection of INH-sensitive TB.