The reason human urine in the bladder is usually sterile is
because it's never exposed to bacteria. The only access
bacteria have to the urine (other than hematogenous spread
or direct injury to the upper urinary tract) is by moving up the
urethra from the skin. But this is difficult to do because three
or four times a day a great gush of urine comes barrelling
through to wash you out. Any bug that's going to colonize
has got to strongly adhere to the epithelial cells to resist
removal, and even then it's an "uphill battle". Urine is a pretty
good growth medium. Certainly nowhere near as good as
what we normally use for media. If that were true we could all
quit buying tryptic soy broth and just use our own
readily-accessible urine. But many bugs will grow to some
extent in urine.
>>> "W Eugene Sanders III" <GatorGene at worldnet.att.net>
01/19/98 02:31pm >>>
Graham Shepherd <muhero at globalnet.co.uk> wrote in
<69vp3v$l93$1 at heliodor.xara.net>...
> The problem is usually to STOP the bacteria growing - urine
> carbon and nitrogen sources, salts, all sorts of other stuff...
>Then why is human urine usually sterile, and bladder
rare? I thought the pH was usually too low, the carbon in a
form that is
energetically speaking relatively inaccessible, and the
the salts high enough to cause dehydration problems. I can
diluted urine outside the body being a fairly good medium for
many kinds of
bacterial growth, but I don't see that being true for undiluted
the relatively anaerobic human bladder.
Alan D. Junkins
Assoc Prof, Medical Laboratory Sciences
Medical University of South Carolina
junkinsa at musc.eduhttp://www.musc.edu/mls/