A Modification of the Fite Formaldehyde (Fite I) Method for Staining Acid-Fast Bacilli in Paraffin Sections

Abstract

For maximal demonstration of acid-fast bacilli in tissue sections it is necessary to avoid sequences of reagents which, first, affect the integrity of the complex upon which acid-fastness depends, and, second, extracts it from those bacillary elements which have been made vulnerable by age or other factors. The greatest damage occurs during dewaxing of paraffin sections by xylene and alcohols; the older and more decrepit bacilli being especially affected. In the technic presented, which is a modified combination of two processes devised by Fite, sections are deparaffinized by a protective mixture of rectified turpentine and heavy liquid petrolatum (2:1) and blotted to water. Staining is with Fite's new fuchsin (magenta III) solution, overnight at room temperature. The sections are then treated with reagent grade formaldehyde, which turns the color of the bacilli deep blue-black, followed by an aqueous sulfuric acid decolorizer, the potassium permanganate-oxalic acid sequence, and a modified Van Gieson counterstain, nuclear staining with hematoxylin being omitted. For total demonstration of all stainable bacilli, restorative treatment in the turpentine-oil mixture before staining is sometimes required, most frequently with leprosy material but also with some tuberculosis lesions.