Isolation of bacteria from yogurt..

Kevin O. Gillies 75031.2064 at CompuServe.COM
Sun Feb 5 00:44:52 EST 1995

Pong Nim:
Isolation of lactobacilli from yogurt is commonly done on MRS medium
(available from Difco) acidified to a pH of 5.5 or Rogosa agar.  
Streak a loop of the yogurt on the plate and incubate at 40C for 24 
to 48 hr.

Isolation  of Streptococcus lactis (now called Lactococcus lactis 
ssp. lactis; L. lactis ssp. cremoris; or L. lactis ssp. lactis 
biovar diacetylactis) from buttermilk is a bit more involved.  If 
your source is commercial buttermilk you will usually find both L. 
lactis ssp. lactis and its biovar diacetylactis.  Given that you do 
not care which, you can isolate the organism on M17 agar (available 
from Difco).  Streak a loop of buttermilk on the plate and incubate 
at 32C for 48 hr or 24 hr if you have access to an anaerobe jar.  

One caution:  Use relatively fresh product for the isolations.  The 
count of these organisms in commercial products can be quite low 
depending on the age of the product. 

Good luck, 

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