Louise

I too have heard of the urban myth of Mycobacteria lurking in tap water, but
personally have never actually seen it and we do a reasonable number of ZNs
on a regular basis., nor do I know of anyone who can prove that they have
actually seen it as well
The point made about not using controls with an abundance of bacteria is
well made, as the vast majority of positive cases will only have a few
bacteria in them, so you need to hunt around a bit for them, so a control
with a few scattered bacteria is more preferable.
As for the point raised by another Histonetter about using different
alcohols, well personally I think that is maybe going a bit too far.
Mycobacterium, as far as I'm aware, don't thrive in alcohol so the risk of
contamination is very small, plus if the sections are taken to water before
staining, they are washed so I would have thought that would further reduce
the risk of contamination to almost zero.
We dewax all our special stains slides on our Leica ST5020 staining machine
where the reagents are regularly changed, plus they are washed in running
tap water.

To my mind the biggest risk of contamination comes from the floating out
water bath following sectioning.
If the water isn't changed on a regular basis you can get all manner of
"creatures" growing in them.
If there is going to be any cross-contamination, that's where it will come
from.

Tot siens en geniet jou dag Louise

Nick Kirk
Histopathology
Hinchingbrooke Hospital
Huntingdon
England


-----Original Message-----
From: histonet-admin@lists.utsouthwestern.edu
[mailto:histonet-admin@lists.utsouthwestern.edu]On Behalf Of louise
renton
Sent: 10 December 2003 08:08
To: histonet@lists.utsouthwestern.edu
Subject: RE: [Histonet] AFB Positive Patient


Kevin,
Hi Kevin,

I have seen a slide of lymph node  from a patient with a severely
immunocompromised state who has such a superabundance of AFB that the
section was visibly pink to the naked eye. Needless to say, these sections
were NOT used as controls for routine work. Interestingly, when PCR typing
was performed, the bugs turned out to M avis and not MTb as initially
suspected.

This is completely  anecdotal, but I have heard of various mycobacteriae
lurking in tap water, that show up on sections washed in that water, causing
"false positives". Has anyone else anything to offer on this possible urban
legend?

best regards



Louise Renton
Bone Research Unit
MRC
Johannesburg
South Africa
Tel & fax +27 11 717 2298
"Time flies like an arrow, fruit flies like a banana"





----Original Message Follows----
From: "kevin williams" 
To: histonet@pathology.swmed.edu
Subject: [Histonet] AFB Positive Patient
Date: Tue, 09 Dec 2003 19:50:24 +0000

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