Leprosy Mailing List – July 16, 2014
Ref.: (LML) M leprae and M tuberculosis acid-fastness
From: Salvatore Noto, Bergamo, Italy
Dear Ben and Pieter,
Thank you for your message (LML July 9, 2014). M. leprae and M. tuberculosis are two acid-fast bacilli. They both show resistance to decolorization by acids but, old leprosy books report that their resistance (acid-fastness) is different.
During a first step of the Ziehl–Neelsen stain they are stained red. Then M. tuberculosis resists to decolorization with 3% hydrochloric acid [and keeps the red colour] while M. leprae resists only to a lower percentage. In this case to avoid decolorization and keep M. leprae red and visible, a 1% concentration is needed.
Old leprosy literature reported this concept. Sir Leonard Rogers and Ernest Muir in Leprosy, Third Edition, London 1946, page 220: “It must be remembered that leprosy bacilli are less acid-fast than tubercle bacilli”. Anthony Bryceson and Roy E. Pfaltzgraff in Leprosy, Third Edition, London 1990, page 63 again reminds the reader of the same. In Leprosy, A Practical Guide, Springer-Verlag Italia 2012, Andrea Clapasson and Silvia Canata, page 58, specifically mention that “Decolorize each slide separately. This is the most critical step of the whole procedure, because M leprae is more easily decolorized than other mycobacteria, for example M tuberculosis. If the duration of the destaining is too long, false negatives may occur, while too short a period could result in false positives”. May be Andrea can comment on this (both on the concentration and the duration of the decolorization)?
Salvatore
LML - S Deepak, B Naafs, S Noto and P Schreuder
LML blog link: http://leprosymailinglist.blogspot.it/
Contact: Dr Pieter Schreuder << editorlml@gmail.com
 | This email is free from viruses and malware because avast! Antivirus protection is active. |
No comments:
Post a Comment