Characterization of differentially detectable Mycobacterium tuberculosis in the sputum of subjects with drug sensitive or drug resistant tuberculosis before and after two months of therapy.

Zainabadi, Kayvan; Walsh, Kathleen Frances; Vilbrun, Stalz Charles; Mathurin, Laurent Daniel; Lee, Myung Hee; Saito, Kohta; Mishra, Saurabh; Ocheretina, Oksana; Pape, Jean William; Nathan, Carl; Fitzgerald, Daniel W

Standard methods for enumerating Mycobacterium tuberculosis (Mtb) in patient sputa can miss large populations of viable Mtb that are unable to grow either on solid media or in liquid media if not extensively diluted. Because these bacteria can be detected in liquid media after limiting dilution, they have been termed differentially culturable or differentially detectable Mtb (DD Mtb). Treatment with isoniazid, rifampin, pyrazinamide and ethambutol (HRZE) for 1-2 weeks has been shown to increase the representation of DD Mtb in the sputum of drug sensitive (DS) tuberculosis (TB) patients. However, little is known about DD Mtb after longer periods of treatment with HRZE, or in patients with drug resistant (DR) TB who receive second-line therapies. Here we measured the proportion of DD Mtb in the sputum of 47 subjects, 29 with DS TB and 18 with DR TB, before initiation of their treatment regimens and at 2 weeks and 2 months thereafter. Prior to treatment, DD Mtb represented the majority of Mtb in the sputum of 21% of subjects with DS TB and this proportion rose to 65% after 2 weeks of treatment with first-line drugs. In subjects with DR TB, DD Mtb was found in the sputum of 29% of subjects prior to treatment initiation, and this proportion remained steady at 31% after 2 weeks of treatment with second-line drugs. By 2 months, DD Mtb was detected in the sputum of only 2/15 (13.3%) subjects with DS TB and 0/15 of subjects with DR TB. One of the DS subjects whose sputum was positive for DD Mtb at month 2 later experienced treatment failure.