Mycobacterium tuberculosis (MTB) is the causative agent of tuberculosis (TB). First discovered in 1882 by Robert Koch, the tubercle bacillus has an unusual waxy coat primarily made up of mycolic acids. Because of its unique cell wall structure, the organism does not retain the usual bacteriological stains and thus is neither a Gram positive nor a Gram negative. Ziehl-Neelsen staining is used instead to detect MTB. Another hallmark of the pathogen is that it grows very slowly compared to other bacteria. Whereas E. coli divides once every 20 minutes, MTB divides once a day. e size of the MTB genome, about 4,000 genes, is similar to that of E. coli. e tubercle bacillus is an aerobic bacillus (i.e., it requires oxygen for growth and is rod shaped). Simple culture media are available to grow MTB in the lab. So is a whole range of experimental animal models, from mice to monkeys, to grow the bacillus in vivo. MTB is a facultative intracellular parasite. It can grow extracellularly as well as intracellularly, both in culture and inside human lesions. Due to the serious disease it can cause, and its way of transmission via aerosol

CONTENTS Disease Manifestations and Treatment 14 A Largely Unmet Medical Need 15 e Challenge of TB Drug Discovery 16 An Atlas for TB Drug Discovery 17 References 17


formation, a Biosafety Level 3 facility is required to work with the bacillus (Cole et al., 1998).