Which of the following statements best explains why M. leprae cannot be cultured on artificial media despite being an obligate pathogen studied since Hansen's era?

• A It undergoes spontaneous transformation into a nonviable L-form outside the host
• B It is killed by oxygen concentrations above 5 percent in vitro
• C Its cell wall prevents nutrient uptake from synthetic media
• D It has a doubling time of approximately 12 to 13 days and highly restrictive metabolic requirements ✓

Explanation

M. leprae has the longest generation time among bacteria, roughly 12 to 13 days, along with a drastically reduced genome lacking many biosynthetic pathways, making conventional culture impossible. It is maintained experimentally in the mouse footpad and in the nine-banded armadillo, whose low body temperature suits the organism. Option C is tempting but wrong because the barrier is metabolic dependence and extreme slow growth, not a physical wall impermeable to nutrients.

Reference: Ananthanarayan and Paniker's Textbook of Microbiology, 11th ed.

High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP

Written and medically reviewed by the StethoPrep medical team.