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I am a 9th grade student from Manila and we're currently working on an investigatory project. We want to know how effective SODIS or solar water disinfection is. The purification method claims to be able to kill pathogen. We've just finished our methodology; we have not done to experiment yet.

There's one thing that concerns us: is it even possible to see pathogen in water using a microscope? We raised our concern to our teacher and at first she believes it is possible. However, she said that she was not sure because she mentioned that some stuff (I forgot what) are "cultured" before checking for pathogen like bacteria.

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Yes your teacher is right. In a microscope you can see microorganisms. Now the question is to identify them as pathogens.

I guess what your teacher has in mind is to use specific culture mediums for different pathogens and see if anything is growing there, then you have a positive.

You could also do a PCR. This is extracting the DNA and amplify specific genes that you know belongs to pathogens.

But the most currently trendy analysis is metagenomics. Basically, you exctract the genetic material from the sample, then sequence and compare against public databases. This methodology allows the identification of everything that is there pathogens and non-pathogens.

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  • $\begingroup$ Thanks for the reply. I'll be honest, my members and I aren't really in to biology nor science itself so we chose a simple project but we really didn't think about how to look for pathogen. $\endgroup$ – Ron Jan 13 '18 at 3:05
  • $\begingroup$ I don't quite understand the two mentioned methods however I think metagenomics might be the easiest to do? Is it as simple as taking a sample of the water, putting it on a petri dish, observing on a microscope, and comparing it to existing microscope images of pathogen? $\endgroup$ – Ron Jan 13 '18 at 3:06
  • $\begingroup$ No it's not that simple. You need to buy for culture media. Different ones for each pathogen you want to identify. You need to find the right protocol for what you are trying to do. In the following link there are several things you can do. Maybe there are some useful hints for you: nap.edu/read/9595/chapter/11#189 $\endgroup$ – aLbAc Jan 13 '18 at 18:59
  • $\begingroup$ If I'm not mistaken, are the "Assay Methods for Waterborne Pathogens" the methods for confirming pathogen in water? I was not able to read the chapter entirely but I at least scanned it. Please confirm if my understanding is correct: To detect pathogen in water, it involves three steps: (1) recovery and concentration, (2) purification, and (3) assaying. Does recovery and concentration mean the "getting of pathogen" in the water? Does purification mean "the removal of unrelated particles in the pathogen?" Does assaying mean the "identification and detection of pathogen?" $\endgroup$ – Ron Jan 14 '18 at 8:27
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    $\begingroup$ I apologize for the swarm of questions but for a group of high school students, what do you think is the simplest method to do this? $\endgroup$ – Ron Jan 14 '18 at 8:29
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Possibly, the simplest test one can analyse a water sample for micro-organisms is a visual analysis using a light microscope (perhaps appropriate for secondary level school inquiry), then proceed to conduct the more complex chemical analyses (usually done in tertiary level school labs) like genetic surveys mentioned earlier. Prepare the water sample in a test tube by centrifuge to cast most if not all elements, bio- and non-bio, to the bottom of the test tube. Using a dropper, obtain a sample from the bottom of the test tube and drop a liquid onto a glass slide, then put a cover glass. Liquid stains are usually applied to the margins of the cover glass using a dropper to aid visualization of the unicellular and multicellular micro-organisms in the water sample. Visual identification of organisms should point the researcher on the next steps to take to obtain a more accurate analysis of the water sample. a good simple protocol for the experiment, as mentioned earlier, should be able to narrow the complex findings of this inquiry.

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  • $\begingroup$ Consider adding references to help the reader $\endgroup$ – have fun Apr 30 '18 at 13:00

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