Abstract
Mycobacteria can be classified as acid-fast and chromophobic. The chromophobic bacilli cannot be stained with carbol fuchsin or counterstain. Both types of bacilli are stained with periodic acid-carbol pararosanilin or periodic acid-methenamine silver. The mechanism of these staining methods depends upon the prolonged periodic acid oxidation of the cells to produce aldehydes and subsequent staining with carbol pararosanilin or methenamine silver. With latter treatment, arylamine can be condensed with aldehydes into Schiff's bases or methenamine silver can be reduced with aldehydes to metallic silver.
In tuberculous or leprous lesions, even after chemotherapy, these methods reveal a large number of bacilli in the lesion, though carbol fuchsin shows few or no bacilli.
The tubercle bacilli can survive in caseation cavity as in vitro, whereas the leprosy bacilli can survive in macrophages and Schwann's cells.
