We’re not alone.

That’s right; use a Q-tip to swab your hand, or the inside of your mouth, and streak the residue on an agar plate. If you incubate it for a day, you will see that there is a veritable world of tiny organisms crawling over the gelatin. Some of them are benign hangers-on, using us as a habitat and source for the dead skin flakes they eat. Others are more insidious, making us sick when they infiltrate our immune system and colonize our bodies. This unit is about the second group, the bacteria responsible for illnesses ranging from mild colds to life-threatening infections. Our focus will be on a forerunner in the war between humans and bacteria, the leading agent of bacterial death the world over: Mycobacterium tuberculosis, the cause of the disease tuberculosis or TB. In contrast to AIDS, this disease was well known to our ancestors, and for many centuries was a major health threat to the world’s population. Advances in bacteriology made more effective treatment of the so-called “White Plague” possible, and TB was initially thought to be conquered earlier in this century. However, the disease has experienced a revival in recent years, rearing its head once again as a potent health epidemic.