Leprosy Mailing List – October 13th, 2011
Ref.: Ziehl-Neelsen or Fite-Faraco staining
From: Clapasson A., Genoa, Italy
Thank you very much to Dr Barreto for his important message (LML Oct. 2nd, 2011). I agree with his conclusions and, I would like adding my comments.
The most important factors, to have a good Ziehl-Neelsen’s or Fite-Faraco’s staining, is the concentration of the primary dye. The staining technique is simple but, there are some pitfalls that should not be underestimated. There are two important factors that each laboratory technician should value remember; they are:
1. The concentration of carbol-fuchsin and phenol: About this please see the attached paper: “Comparison of variants of carbol-fuchsin solution in Ziehl-Neelsen for detection of acid-fast bacilli”. Selvakumar N, Sekar MG, Rahman F, Syamsunder A, Duraipandian M, Wares F, Narayanan PR. Int J Tuberc Lung Dis. 2005 Feb;9(2):226-9.
2. The duration of the discoloration: False negatives increase with excessive time of decoloration. In Genoa I decolorize each slide separately with 2,5 ml of solution of hydrochloric acid (95ml ethanol 96° and 1ml hydrochloric acid 37% (fuming)), but if it is difficult the acquisition of “alcohol absolute” it is possible to use an aqueous solution of 23,75% sulphuric acid and 3% alcohol.