Importance of determining viability of Mycobacterium leprae inside macrophages—an in vitro method using uracil.

It has been demonstrated that Mycobacterium leprae, are capable of taking up uracil and incorporating it into trichloroacetic acid-insoluble materials, both as free suspension of bacteria, as well as when they are inside the macrophages, a host cell for their in vivo survival. Same amount of bacteria show better incorporation inside macrophages than as free bacterial suspension. Both types of incorporation are inhibited by rifampicin an antileprosy drug and an RNA synthesis inhibitor. Thus uracil uptake by Mycobacterium leprae inside macrophages has been used for standardising a rapid in vitro viability assay for the leprosy causing bacteria.