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,
Kevin
