Which test results after 3 weeks of incubation on Lowenstein-Jensen agar are consistent with Mycobacterium tuberculosis?

The presence of niacin production, along with nitrate reduction and the absence of photochromogenic characteristics, supports the identification of Mycobacterium tuberculosis. Mycobacterium tuberculosis is known to produce niacin, which is an essential metabolic indicator of this particular bacterium. Nitrate reduction is also characteristic of M. tuberculosis, as it can reduce nitrate to nitrite.

The absence of photochromogenic activity further aligns with M. tuberculosis, as this species does not demonstrate pigmentation when exposed to light, unlike certain other mycobacteria that do. Together, these specific test results provide a reliable identification for M. tuberculosis after the incubation period on Lowenstein-Jensen agar, which is a selective medium for the growth of mycobacteria.

The other options provided do not represent characteristics typically associated with Mycobacterium tuberculosis, further solidifying A as the correct answer.