Drug susceptibility profiles – pyrazinamide (PZA): Which mycobacterial species listed is characteristically susceptible to pyrazinamide under standard testing conditions, aiding in species differentiation within the M. tuberculosis complex?

Introduction / Context:
Pyrazinamide is a first-line antitubercular drug active in acidic environments, particularly effective against semi-dormant bacilli. Recognizing which species are susceptible versus resistant assists in both therapy and species-level differentiation inside the M. tuberculosis complex.

Given Data / Assumptions:

• Mycobacterium tuberculosis is generally PZA-susceptible unless resistant mutants are present.
• Mycobacterium bovis is inherently PZA-resistant due to pncA-related differences.
• Many non-tuberculous mycobacteria, including MAC and rapid growers, are not reliably susceptible.

Concept / Approach:
PZA susceptibility helps distinguish M. tuberculosis (susceptible) from M. bovis (resistant). PZA is a prodrug converted to pyrazinoic acid by pyrazinamidase; functional differences in this enzyme drive the susceptibility profile. Rapid growers and MAC species typically show intrinsic resistance and are not treated with PZA in standard regimens.

Step-by-Step Solution:
Recall species-specific PZA profiles. Exclude M. bovis and most NTM as resistant/non-reliably susceptible. Select Mycobacterium tuberculosis (susceptible). Link to clinical regimens where PZA is included in intensive phase.

Verification / Alternative check:
Guideline-based regimens for drug-susceptible pulmonary TB include PZA, contrasting with treatment of zoonotic TB due to M. bovis where PZA is omitted.

Why Other Options Are Wrong:
M. bovis is classically resistant; M. fortuitum and MAC organisms are not targeted with PZA.

Common Pitfalls:
Assuming all “TB bacteria” are PZA-susceptible; species-level distinctions matter.

Final Answer:
Mycobacterium tuberculosis (susceptible).