Need Biolog help.

Enigl enigl at
Fri Sep 6 15:09:37 EST 1996

In article <50arke$1bb at>, kbiggs at (Keith)

>Subject:	Need Biolog help.
>From:	kbiggs at (Keith)
>Date:	1 Sep 1996 02:15:42 GMT
>We have recently acquired a Biolog microstation, and are having problems 
>getting good clean identifications with gram positive organisms. Has
>had any similar problems? I have been using both TSA and TSA w blood ,
>both give equally poor results. Specifically, a colour change occurs in
>all of the wells, making visual ID difficult. Any suggestions? Your help
>be greatly appreciated. Keith

The dye used is a metabolic indicator.  It could be indicating
contamination with a non-pure culture or chemical contamination that is
letting the pure culture grow when it should not be able to grow.

If a mixed culture is unknowingly used or contaminating microorganisms
(remember yeasts and mold too)  get into the wells, the dye will turn. 
The most common source is the diluent used.  Have you done a sterility
test on your diluent?  Have you tried rehydrating without adding a culture
to test the sterility of the system?


Validation of microbial identification system is becoming a concern of the
FDA.  The next time you are audited you should have a written validation
protocol available for review.  Questions like this are what the FDA is
afraid is happening.  In many cases the ID is not critical and will not
affect any critical control point, BUT, why let it happen.  During
validation you can workout these problems.  I hope the manufacturer has
been of some help.  My experience with Vitek has been a very good one and
I am asked to validate Viteks quite frequently lately.  I hope Biolog has
done as much as Vitek has to ease validation.

Here are some tips that have worked for me with Vitek:

1.  Use only fresh isolates.  If ATCC, rehydrate streak two times on TSA
for G+ but no more.   Other than ATCC, make very few subcultures (e.g.,
2.  Standardize on one media supplier, variation in TSA proteins have
caused problems.
3.  Prewarm everything you can to 35 degrees C.  Room temperature is not
warm enough.  Diluents, media, cards, everything...
4.  Improve the standardization of the inoculum level.  Most technicians
have too much variation.  You can test this by running 3 cards from one
inoculum source and then making us another source and running it three
times.  The ID will be different if the two sources were not standardized.
5.  G+ have a problem with suspension, they floculate.  I shake the tubes
instead of vortexing. Vortexing is less effective.

I could go on but try these first. Contact me if you want to.


Davin C. Enigl, MS-MEAS, President-Microbiologist
HACCP Validations-sm  Hazard Analysis and Critical Control Points for the
Food, Cosmetic, Pharmaceutical, and Nutritional Supplement Industry
Voice: (916) 989-8264,  Fax: (916) 989-8205,  Pager: (714) 725-7695
9040 Erle Blunden Way
Fair Oaks, CA 95628
September 5, 1996
4:46 pm

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