Phenotypically Adapted Mycobacterium tuberculosis Populations from Sputum Are Tolerant to First-Line Drugs

Tuberculous sputum contains multipleMycobacterium tuberculosispopulations with different requirements for isolationin vitro These include cells that form colonies on solid media (plateableM. tuberculosis), cells requiring standard liquid medium for growth (nonplateableM. tuberculosis), and cells requiring supplementation of liquid medium with culture supernatant (SN) for growth (SN-dependentM. tuberculosis). Here, we describe protocols for the cryopreservation and direct assessment of antimicrobial tolerance of theseM. tuberculosispopulations within sputum. Our results show that first-line drugs achieved only modest bactericidal effects on all three populations over 7 days (1 to 2.5 log10reductions), and SN-dependentM. tuberculosiswas more tolerant to streptomycin and isoniazid than the plateable and nonplateableM. tuberculosisstrains. Susceptibility of plateableM. tuberculosisto bactericidal drugs was significantly increased after passagein vitro; thus, tolerance observed in the sputum samples from the population groups was likely associated with mycobacterial adaptation to the host environment at some time prior to expectoration. Our findings support the use of a simpleex vivosystem for testing drug efficacies against mycobacteria that have phenotypically adapted during tuberculosis infection.