Cryptosporidium and Giardia Source Water Monitoring

This week in lecture we began covering material on protozoan parasites, which can cause a variety of diseases and can be harder to detect in the laboratory than other organisms such as bacteria.  In an attempt to take a slightly different angle on the subject, I thought that going over how some species can be monitored/detected in the environment would be beneficial. 

For the past seven years prior to entering the program, I worked as a biologist for an environmental testing laboratory, which participated in the EPA source water monitoring study of systems for Giardia and Cryptosporidium. During my time there I analyzed over 3,000 samples, so you could say that I somewhat familiar with the process.

The method is long, labor intensive, time consuming and could take up to a week to complete.  In general, a large sample of water is concentrated to just a few drops on a slide which is then stained and examined microscopically.

First, a roughly 10 liter sample of source water (which is the lake, river, etc that a water processing plant pulls from to make drinking water) is collected and filtered through a specialized filter that has pores small enough to catch the desired organisms.  Next, a soapy solution is added to the filter, which is then shaken to remove and resuspend any collected material.  This solution is then centrifuged to concentrate the dirt and any organisms into a pack pellet.  Then the supernatant is removed, the pellet is resuspended, and transferred to a small tube.  Next, a solution containing small iron beads coated in anti-Crypto and anti-Giardia antibodies as well as pH buffers are added to the tube with the sample.  The beads will grab onto the organisms, and in the presence of a magnet, allow the potential organisms to be separated from the remainder of the contents of the sample.   This process can then be reversed by the addition of acid, which elutes the organisms from the beads into the eluate and onto a microscope slide.  This can then be stained with fluorescent dyes and examined for the presence and enumeration of the cysts and oocysts which may be present.

For the EPA study, water systems were required to send these samples in once a month for two years.  After the required monitoring was completed, the data could be compiled to calculate the number of cysts/oocysts per liter which could be correlated to a risk for these organisms to contaminate the drinking water produced by the individual water system. 

Hopefully this was not too boring, but I thought that it would be useful for others to know how these organisms are detected from environmental samples in addition to their detection in human samples.