Which statement about Mycobacterium leprae is true?

• A. It is easily grown in culture
• B. It is difficult to grow in vitro
• C. It is a virus
• D. It is a yeast

Answer: (B)

Mycobacterium leprae is a bacterium that causes leprosy and is infamous for its extremely slow and difficult growth in the lab. Unlike many bacteria, it cannot be grown on standard artificial culture media in vitro; it requires living host tissue or animal models, such as mouse footpads or nine-banded armadillos, to multiply. This long generation time and dependence on host environments make cultivation in routine lab media impractical, which is why it’s described as difficult to grow in vitro. It is not a virus or a yeast—it's an acid-fast bacterium in the Mycobacterium genus with a lipid-rich cell wall.