how to count bacteria within within pure bakery yeast?

Chris & Jen Procyshyn procyshyn at
Mon Jun 22 22:30:45 EST 1998

There are numerous ways to determine bacterial contaminants within
Saccharomyces spp. The most often used method of culture yeast inhibition is
the addition of cycloheximide (rate of 100 pmm, but will depend on cell
titre) to a standard medium supportive of the contaminant recovery. In
addition, some (but not all) strains may be temperature intolerant above
37deg C. Possibly this temperature will be selective as well, however I
caution you to check with a purified isolate of culture yeast and verify the
temp with a calibrator.

Also, depending on the organisms you wish to recover, you may wish to use a
more nutritive media. Typically, lactic-acid bacterium and other commonly
found yeast contaminants are quite fastidious and will require a complex
nitrogen source. For these, I would suggest MRS agar, or possibly WLN
(broth...possibly as an enrichment step? or agar). The expectant organism is
your first consideration for media selection, especially in this case.

Beyond this, I suggest you consult any number of fermentation microbiology
texts as much work has been done in this area for numerous applications.

C. A. Procyshyn
Sr. Microbiologist
Stroh Brewery Company
La Crosse, WI, 54601
procyshyn at

Rainer Hofmann wrote in message <3586A157.1F6A8EF9 at>...
>we want to determine total amount of aerobe mesophilic bacteria which
>may be natural part of pure yeast used in bakery.
>Any ideas of supplements or medias we could use to supress growth of
>yeasts? My idea is to add an anti-mycoticum to a simple plate-count

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