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 labeled N(2) gas formed specifically from labeled INH by mycobacterial KatG enzyme. In vitro data shows the assay is specific, dependent on mycobacterial abundance, and discriminates between INH-sensitive and resistant (S315T mutant KatG) TB. In vivo, the assay is rapid with maximal detection of (15)N(2) in exhaled breath of infected rabbits within five to ten minutes. No increase in (15)N(2) is detected in un-infected animals, and the increases in (15)N(2) are dependent on infection dose. This test may allow rapid detection of INH-sensitive TB.