No Growth-to-TNT Count Question

Enigl enigl at
Fri Jun 26 14:17:58 EST 1998

In article <1998062515202600.LAA10610 at>, genomejb at
(GenomeJB) writes:

>A dialysis unit submitted at "Total Count" Sampler to its reference lab.
>24 hours, result was "No Growth"; after 48 hours, result was
>Dialysis unit has never had such a result before. Lab error, or real
>if real, what are the possibilties?

Water bateria are slow growers and require a minimum of 48 hours in most cases.
 Maximum counts occur after 5 to 7 days of incubation according to the US legal
method published in _Standard Methods for the Examination of Water and

Your lab has no business reporting 24 hour counts -- worthless.  Unless . . . 
I do not think they would be using my 24 hour injury recovery method because it
is not a standard method (yet).

Water systems are tricky.  The best standard method I have used is R2A with
20-30C incubation for 7 days with a sample size of 10, 100, and/or 1,000 mL
filtered through a membrane filter.  Your industry will have it's own legal
methods.  There are eight water culturing methods that I recall.  Each has pros
and cons. 

The chances your system has a biofilm is very good if you got TNTC.  Biofilms
form in the system and are difficult to detect unless you scrape the inside. 
Taking flowing water samples only gets the part of the biofilm that is falling
off -- usually very hard to detect unless you have a very sensitive method
(e.g., 1,000 mL filter method).

If you lab used hot agar pour plate on a poor medium like PCA (TSA is illegal
for your industry, I'll guess. I hope they did not use that) and only 1mL
sample size . . . That is a bad method.  It will not detect a biofilm until it
is TNTC and too late.  My advise: change to a more sensitive legal method.

TNTC is NOT consistent with "lab error." Lab error is low level gram positive
coccus, not TNTC.  No way.  Think about it, you would never assume lab error
for a "good" result.  If the lab would have been in error, maybe the "good
results: were wrong.  No, you can not assume lab error.  

You most likely really DO have a biofilm problem.  Clean by dissassembly then
sanitize.  You RO membrane is most likely biofouling. 

I charge $600 for a consulting project like this.  If you need me call
916-989-8264.  See my web site at
Davin C. Enigl, MEAS. Microbiology Consultant for Foods, Cosmetics,
Pharmaceuticals and Biotechnology. FDA validation protocols, water system,
autoclave, facility start-up. Author: _Preservative-Free and Self-Preserving
Cosmetics and Drugs_ Marcel Dekker.

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