[John Doubell]

John Doubell  asked the Naked Scientists:
   A friend once told me that if I cut myself in the bush and had no water I could clean the wound with my urine, as it (urine) is sterile. Was he correct?
What do you think?

[Chemistry4me]

Except in cases of kidney or urinary tract infection (UTI), urine is virtually sterile and nearly odorless.

Urine has also been historically used as an antiseptic. In times of war, when other antiseptics were unavailable, urine, the darker the better, was utilized on open wounds as an antibacterial.

http://en.wikipedia.org/wiki/Urine

Take your friends advice  []

[SquarishTriangle]

Urine directly from the bladder is normally sterile. However, on its passage from the bladder to the outside world, urine becomes contaminated by bacteria normally present in the lower urethra and external genitalia. So by the time it gets to your wound, it will already contain bacteria. While intact skin may provide an effective barrier to infection by those bacteria, a pre-existing breach in the barrier (ie. the wound) may be just what is needed for an opportunistic infection to occur.

[chris]

Squarish triangle is absolutely right; urine is produced sterile but can pick up bugs along the way. However, urine collected from circumcised men is usually also sterile owing to the absence of the foreskin, which is colonised by bacteria at high density.

[cheerio]

What about female urine? How sterile is it in comparison to a circumcised male?

[chris]

When women provide urine specimens they should always be encouraged to part the labia so that the stream is collected "clean catch"; this is because the vulva carries a large commensal bacterial load. These bacteria are not necessarily harmful - in fact they include specialised types (lactogenic bacilli) that acidify the vagina and thus help to suppress the growth of less desirable colonisers such as yeasts and faecal bacteria. But there are also small numbers of potential pathogens, like E. coli, and if the urine is allowed to pass across the mucous membranes of the labia before being collected then it can pick up these bugs, making it impossible for the microbiologist to discriminate carriage organisms from those that were genuinely causing a urine infection.

So, to answer your question, for the anatomical reasons explained above, women's urine (once it has exited the body) is probably less likely to be sterile than urine collected from a circumcised male.

Chris

[JnA]

women are often told to take a 'midstream' sample.. is this for the same reasons and you state Chris?

[chris]

Sorry for the late reply - only just saw this.

The answer is yes. The theory goes that if you pass some urine first any detachable bacteria that are colonising the urethral opening or have begun to ascend the urethra will be washed away; the "mid-stream" should therefore be relatively free from these potentially misleading contaminants, giving a more reliable culture or microscopy result.

Chris

[LeeE]

A friend once told me that if I cut myself in the bush and had no water I could clean the wound with my urine, as it (urine) is sterile. Was he correct?

Depending on the nature of the wound, you might be better off not 'cleaning' it at all.  The flow of blood coming out of the wound is quite good at stopping bacteria from getting in to the organism, and once the blood has scabbed it forms quite an effective barrier.  As the blood starts to thicken and dry outside of the wound it becomes harder for bacteria to move through it and enter the organism but 'cleaning' or removing this blood can make the wound more susceptible to infection.

Licking the wound may also help, even though our mouths are full of bacteria.  Luckily, the stuff that resides in our mouths isn't likely to result in an infection in other parts of the body and may even try to start digesting 'foreign' bacteria.

Sometimes evolution comes up with some rather elegant solutions.