I'm a undergraduate biology student working on my senior thesis. Read on
if you are interested, or want to comment on my methodology. I
hypothesize that when you feed a baby a bottle of breastmilk, you can
safely store unused portions in the refrigerator for 5 days.
Clarifying the term "safely" is my first dilemma. First of all there are
currently no commonly accepted standards. I found at least three
different requirements for "safe" milk. 1) Total CFU/ml under 10,000,
with no enteropathogens. 2) Total CFU/ml under 100,000 excluding S.
aureus, group B strep, pneumonoccus and coliforms. 3) Total CFU/ml under
25,000 with S. aureus under 1000. All of these requirements are set up
by different milk banks, who supply breastmilk mainly to ill, preterm
infants. There are currently NO guidelines for full-term healthy
infants. I just randomly chose number 2, because it clearly let me know
what I needed to test for.
For my methods, I will have 6 breastfeeding women and their infants come
to the lab at my school. They will pump four ounces with a clean (not
sterile) electric pump.* I will save 2 ounces as a control, and put the
other 2 ounces in a bottle. The child will eat for one minute, or 1/2
ounce (whichever comes first). *It was important to emulate normal
pumping and storage conditions, therefore I used "clean" techniques for
collection, and sterile techniques for plating, identifying etc.
I will do standard plate counts, as per my microbiology manual, using
tryptone glucose extract agar. I will also plate 100 µl of milk on
mannitol salt (Staff), blood (strep, and pneumonoccus), and McConkeys
I have already performed a pilot study, with three participants,
performing Standard plate counts every 6 hours for two days. I found
that there was a average of 9000 CFU/ml in the used milk at zero time.
This number dropped to about 1000 CFU/ml at 48 hours. The control milk
had an average of 6000 CFU/ml at zero time, and dropped to 0 CFU/ml at
48 hours. I haven't researched the drop in bacteria rate, but I think it
has to do with products of lypolysis, and their inhibitory affect on
Anyhow, this is my experiment. I am planning to do it around the end of
January, so if anyone has any suggestions, please let me know before
rbruss at ix.netcom.com