mol13 at msus1.msus.edu
mol13 at msus1.msus.edu
Fri Sep 23 12:24:34 EST 1994
I have just noticed the thread on BHI medium and I would
like to offer my speculation concerning as one person put
it "what is its magic ingredient?".
As my work concerns the ability of various neuroendocrine
hormones to influence the growth and pathogenicity of bacteria,
notably gram-negative, I have always found it curious that the
question of BHI's ability to support bacterial growth has not
been investigated to a high degree. At the ASM meeting in New
Orleans a couple years ago I brought up this point during my
presentation when I discussed the ability of neuroendocrine hormones
associated with stress to greatly increase the growth of E. coli as
well as P. aeruginosa (the medium I use is a serum-supplemented media).
Could it be more than just coincidence that the two major components
of BHI, namely calf brains and beef hearts, come from the two highest
innervated organs in the body? Do various neuroendocrine hormones
survive the processing steps as well as subsequent autoclaving? The
answer is most definitely yes (we have even seen norepinephrine peak in
HPLC-EC we have run on autoclaved BHI).
I have in fact called the product quality manager at Difco and asked
rather naively how is BHI made. His answer was that you didn't need
a degree in rocket science -- you take 100 lbs. of beef hearts and 100
lbs. of sheep brains, squish 'em down (his words), filter, dehydrate and
sell it. I then asked if he ever sees differences in growth properties between
various lots of BHI and his answer is all the time. The lots just have to
meet some minimum requirement.
Considering the fact that the hearts and brains are coming from different
slaughterhouses where the animals are undergoing a very stressful procedure
you may be ending up with lots of organs exhibiting different levels of
neuroendocrine hormones which eventually make it to your lab. And by
the way, media derived from plant material also contains numerous
hormones since plants themselves are great reservoirs of such neuroendocrine
hormones that we usually only associate with mammalian species.
One final thing, and then I'll get off my soapbox, can one assume that the
bacteria growing happily in BHI (where everything it can want is provided)
are the same as bacteria in a host where numerous selection pressures are
operative? Just remember the decades-long known difference between in vivo
and in vitro passaged bacteria in terms of virulence.
Department of Biological Sciences
Mankato State University
e-mail: MOL13 at msus1.msus.edu
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