Evaluating the performance of basic fuchsin for the Ziehl-Neelsen stain

An investigation of commercially available basic fuchsin (BF) dye powders used for the detection of acid-fast bacilli (AFB).

To determine whether single, or multiple, assays may predict the performance of BF in the Ziehl-Neelsen (ZN) method.

The composition and staining properties of six BF dye samples were assessed using continuous recording spectrophotometry, reverse phase thin-layer chromatography (RPTLC) and a standardised ZN biological staining test.

Variable proportions of BF homologues could be demonstrated in the samples, but neither spectroscopy nor RPTLC was fully predictive of their staining quality. ZN staining of standard smears was needed to identify five powders that yielded satisfactory results and one powder with unsatisfactory performance. Increasing the BF concentration did not always result in improved staining.

Simple analytical methods, such as spectrophotometry and RPTLC, should be complemented by biological staining of control smears to assess the quality of BF dye powders. This allows tuberculosis control programmes to avoid procurement of BF dyes that would fail to detect AFB even when strictly adhering to current international guidelines for ZN staining.