Introduction to some aquatic protozoa in Essex
thanks to the introduction of proper sewage controls.
Certain mammals can carry micro-organisms that can be pathogenic in man. The common brown rat
is one such animal. Rats frequent freshwater habitats and will urinate into the water and pass into the
pond or river a bacterium called Leptospiraea. This bacterium is a spirochete and is best seen with
the aid of dark field microscopy where they reveal themselves with their characteristic spiral shape.The
size range of this type of bacteria can range from 5-500mm in length.
People who use the water for recreation run a risk of catchmg Weill's disease. The spirochete can
enter the body via cuts, eyes, nose and swallowing through the mouth. It must be stressed that this
disease is very rare in England. When searching for bacteria with the microscope it is always preferable
to use either dark field or phase contrast in order to render distinct the micro-organism from the
background. Also remember to treat all micro-organisms as potential pathogens. Below is an example
of an unidentified fresh-water spirochaete taken with a x4() phase contrast objective in place.
Figure 9. A freshwater spirochaete under x40 phase contrast © Steve Durr
Learning more
These are just a few of the many inhabitants of a fresh water pond that can be caught and examined
quite easily by anyone who has access to a microscope. I appreciate that a new microscope can cost
between £500- £1000 but this investment will last a lifetime and, as I hope I've shown, will repay
itself many times over.
If you are interested in learning more about microscopy and microscopic pond life you can visit my
Web site wvvw.durr.demon.co.uk. This site contains many more photographs of pond micro-organisms
in colour and black and white. If you would like to ask further questions or arc interested in starting
out on this fascinating subject you can contact me on telephone 0208 989 4553. E- mail
steve@duiT.demon.co.uk.
(Note: One micrometer = 0.001 of a millimetre. (Abbrev = mm))
Essex Naturalist (New Series) 18 (2001)
37