(LML) M leprae and M tuberculosis acid-fastness

Leprosy Mailing List – July 16,  2014 

Ref.: (LML)   M leprae and M tuberculosis acid-fastness

From:  Salvatore Noto, Bergamo, Italy

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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

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LML - S Deepak, B Naafs, S Noto and P Schreuder

LML blog link: http://leprosymailinglist.blogspot.it/

Contact: Dr Pieter Schreuder << editorlml@gmail.com

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