Science Questions

How do bacteria know where they are in your body? Things like cholera infect your guts. How do they know to get there? Andy Steed

It’s all because bacteria have what’s called a tropism.  They are set up or they are specialised in order to survive in certain environments.  They might have, for instance, molecular grappling hooks which are called pili.  These are the bacterial equivalent of Velcro®.  It allows them to stick on to certain tissues.  Different tissues in our bodies have different chemical environments.  If you look at say, your bladder and the urethra people get urine infections because specialised forms of E. coli called uropathic E. coli can stick onto the wall of the bladder and also onto the urethra.  Then your body tries to prevent them from doing that by having this sort of anatomical Teflon® in the form of very slippery cells.  The E. coli have very strong Velcro® which enables them to stick.

Other bacteria would just be washed away. In the blood stream there are some bacteria that could cling onto the heart valves.  They can do that because they’ve developed an ability to recognise the surface of the heart valve, stick on and then secrete this thing which is called a biofilm: a protective layer which stops the immune system getting at it.  It’s not so much that they know where to go.  It’s more that by chance they find themselves in the right place and they have the ability to stick on and make a home there.  Different bacteria thrive in different environments because they’re specialised to exist in those particular places.

June 2008