A laboratory scientist attempts to culture Mycobacterium leprae from a slit-skin smear sample using standard solid and liquid media. All cultures remain sterile after 12 weeks. Which property of M. leprae best explains this failure?

• A It is an obligate intracellular pathogen destroyed by sodium hydroxide decontamination
• B It grows only at 42 degrees Celsius, which standard incubators do not achieve
• C It requires mycobactin supplementation in the medium for growth
• D It has never been reliably grown on artificial media and multiplies only in the mouse footpad and the nine-banded armadillo ✓

Explanation

M. leprae cannot be cultured in vitro despite decades of attempts. In vivo multiplication occurs in the mouse footpad (Shepard's model) and heavily in the nine-banded armadillo, which is used to produce lepromin antigen. Its generation time of about 13 days, the slowest among bacteria, further limits any growth. Mycobactin requirement applies to M. avium paratuberculosis, not M. leprae.

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.