Evaluation of variants of carbol fuchsin solution to stain acid-fast bacilli in-situ by the pot method.

Abstract

Ziehl-Neelsen (ZN) staining requires heating, and pre-stained smears contain viable bacilli. To evaluate four variants of carbol fuchsin solution by the pot method and compare the results with ZN staining, taking culture as gold standard. Five hundred sputum samples from presumptive tuberculosis cases were homogenised and divided into two parts. One part was subjected to routine ZN staining and culture on solid medium, the other was equally distributed into four pots. Equal quantities of the basic fuchsin (BF) variant were added to each pot. Variant I contained 2% BF with 10% phenol and 4% ammonium sulphate (PhAS), while Variant II had 0.6% BF with PhAS; Variants III and IV contained respectively 2% and 0.6% BF with 10% phenol only. After 1 h, smears were made from each pot and culture was performed on Löwenstein-Jensen medium. Smear results were compared with the ZN results and evaluated against culture. Variant III gave excellent results compared to ZN (κ = 0.97), with sensitivity, specificity, and positive and negative predictive values similar to those of ZN, taking culture as gold standard. Pot contents were negative for Mycobacterium tuberculosis culture.