From:Bert Dotson <>

Bob Richmond asks:

Acid fast variants such as the Fite-Faraco
technique require a M. leprae control - does anyone on this list know where 
to get these?

In our hands Nocardia is more difficult to stain than M leprae--we also 
tend to see it more often. When Nocardia is properly stained M leprae 
invariably stains well. The converse is not true. We use Nocardia for our 
standard control when a Fite stain is requested.

Is MAI a suitable
staining control for M. tuberculosis, and vice versa?
Once again, I can only speak from our experience but the answer is both yes 
and no and this largely depends on the experience of the screener and the 
way a director chooses to view controls. We use MAI for our acid fast 
control but we have a small supply of M. tuberculosis for special requests. 
All the MAI control tissue we have comes from autopsy and tends to be 
loaded with organisms. This leads to difficulty training technicians the 
importance of a pale counterstain--the MAI in our control will stand out 
strongly even when the counterstain is dark enough to mask M. tuberculosis 
in most cases. Residents in training may also look at the MAI control and 
underestimate the screening effort required for M. tuberculosis. On the 
positive side, you don't have to waste much time determining the stain 

Bert Dotson

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