Staining mycobacteria with carbolfuchsin: properties of solutions prepared with different samples of basic fuchsin.

Acid fast staining of mycobacteria in the form of beadings is obtained by means of a carbolfuchsin solution (Ziehl-Neelsen stain) prepared from pararosaniline or from certain kinds of basic fuchsin. After such acid-fast stains, the intensity of the bacilli's colouring was rather poor and unstable, so that some bacilli lost their acid-fast stain. In contrast, an acid-fast staining of mycobacteria in rod form results by using a carbolfuchsin prepared from rosaniline or from other basic fuchsins included new fuchsin. The spectrophotometric and thin-layer chromatographic data indicate that the main component of those basic fuchsins showing beady staining may be pararosaniline, whereas the main ingredient of basic fuchsin with staining the bacteria in rod form may be its higher homologues. Neither chloride nor acetate of the fuchsin could affect the appearance and number of stained bacilli. The commercially available "basic fuchsin" is either the chloride or acetate of pure pararosaniline or consists of variable mixtures of it with higher homologues. Consequently, only a basic fuchsin which has an absorption maximum at lambda greater than or equal to 552 nm could be employed for the acid-fast stain of mycobacteria in a stable manner. Pararosaniline included some basic fuchsins, composed mainly from pararosaniline, should not be selected for the preparation of the carbolfuchsin formula.